Here's my best attempt. I was going to make this an ask, but I have too many videos and images to ignore them. I'm happy to go into the history behind the ship wars as far as I can.
I will note that I personally am a Zutara shipper, and most of my understanding of the ATLA ship wars is passed down from people who ship Zutara. Thus, I might be biased to a degree, and I'd encourage you to hear from others as well. I'll try and organize this into sections.
Point 1: Zutara was ship-baited when the show was airing
Okay, so, to start with, I think it's important to note that the ship wars were absolutely fueled by Nickelodeon at the time ATLA was airing, and they show was not airing with Kataang as a guarantee. That might not be obvious to someone watching the show later, but there were magazines with games about who Katara would end up with.
(Note also the choice to have Zuko saying one of the most iconic Zutara lines, especially pre-season 3)
Even things like the trailers were absolutely cut with this in mind:
If you go to the 40 second mark, for instance, you see how they cut from Katara recoiling from Aang's kiss, over to the Zuko and Katara hug, and it absolutely elicits cheers.
Point 1b: Zutara was at least discussed as a possibility
Furthermore, despite what's commonly claimed nowadays, it was absolutely debated to some extent what the final pairings would be. As much as we all dislike M. Night Shyamalan's movie, he has absolutely no reason to be biased, and there are a few other quotes, all from one paragraph on Katara's wikipedia page:
In the Avatar Extras for "The Avatar Returns" it is stated that "Zuko was originally going to be the love interest for Katara",[15] and in "The Ember Island Players" it is stated that "the creators and writers toyed with the idea of Zuko and Katara falling in love".[16] Co-creators Michael Dante DiMartino and Bryan Konietzko deny that they ever considered Zuko and Katara getting together, and claim that Katara becoming a couple with Aang was planned from the start.[17][18] However, the initial proposal of the series as outlined in the development bible does not have Katara enter a romantic relationship with anyone, directly countering their claims that Katara was always intended to end up with Aang.[14] Multiple writers who worked on the series have also made statements contradicting the co-creators. Writer John O'Bryan said that the topic of Zuko and Katara becoming a couple came up a lot in the writers' room.[19] This is corroborated by writer Joshua Hamilton who says that the crew argued about who Katara should be with, and that there was a plan where Zuko and Katara ended up together.[20] When reflecting on the writing process for The Ember Island Players, writer Tim Hedrick stated that Katara's rejection of Aang's romantic advances and the allusions to a potential relationship between Zuko and Katara in the episode allowed the writers to keep their options open, as Aang and Katara becoming a couple in the series finale was not a foregone conclusion, and Aang could have remained single.[21] This aligns with comments made by M. Night Shyamalan, director of The Last Airbender film, who recalled that during the production of Book Three: Fire, DiMartino and Konietzko were uncertain, "At that time they hadn't even decided where things were going to end, even like who Katara was going to end up with."[22]
Also, here's an earlier script for The Southern Raiders where the term Zutara is explicitly referenced:
Anyways, you might note that Bryan and Michael (often referred to as Bryke) deny that Zutara was ever a possibility. They're going to come up a lot in this explanation, unfortunately. A lot of Zutara shippers dislike them, for not unreasonable reasons.
So, you've got all this division in the writers room, where both ships have some support.
Point 1c: People genuinely thought it might happen
And then, going into the finale, you have an honestly really strange in hindsight run of these episodes, which literally have an argument between Katara and Aang every episode (over Aang's idea of forgiveness and Katara's desire for confronting Yon Rha in The Southern Raiders, over Aang non-consensually kissing Katara in The Ember Island Players, and then over killing in Sozin's Comet), none of which are actually resolved on screen. One of them storms off and that's it. And in the meantime, Katara and Zuko are getting closer, sitting next to each other, providing each other support, and then Zuko literally takes a blast of lightning to save Katara, with their key bits of the finale directly involving each other.
Obviously, then, it was a bit surprising when things ended up Kataang for shippers on both sides at the time, and I do think that alone would have probably lead to some bad blood from Zutara shippers against Kataang and Kataang shippers, at least at the time. Honestly, I wouldn't be at all surprised if Zutara shippers did some pretty shitty things at the time, I'm not trying to pretend that one side is entirely innocent.
Point 2: The SDCC 2008 Book 4 incident
But I don't think it would have been nearly as bad/lasting as it is, if not for the Book 4: Air incident at SDCC 2008:
Now, to be clear, I understand this was meant to be a joke. But frankly, using fanart made by people who really loved the show, many of them possibly children, in order to make fun of them? Writing "Thanks for all some MOST of the fanart through the years"?
It just strikes me as wrong, especially when it then crossed the line into attacking real people by saying "Women who think that Zuko and Katara should be together will forever have doomed relationships". (Also, note the specific targeting of women. Zutara is often attacked as a self-insert ship for women, or on the idea that it's a female fantasy, and I do think the hate for it is oftentimes gendered, though less so nowadays, or at least less explicitly so.)
Anyways, this is what really set Zutara shippers against Bryke, but at the same time, it kind of set the tone going forwards of how Zutara shippers should be treated. The showrunners had declared open season on Zutara shippers, and a lot of the fandom kind of ran with it.
Point 3: Seriously, can we go back to that non-con kiss?
Of course, that's not the only reason Zutara shippers are targeted. Part of it is also that Zutara shippers often believe that Zutara being the canon (or implied canon with no explicit ships) ending would have actually been better, and often critique how Kataang is written in canon. They often dislike how it's very much a 'Hero gets the girl' ending, with no explanation or real examination for how Katara feels beyond her suddenly changing her mind from being confused to kissing Aang. It feels especially egregious when Katara is essentially portrayed as coming around after Aang forcibly kisses her, and feels like it's giving a bad message: it's okay to forcibly kiss a girl and persistently pursue her, she'll come around eventually.
Making matters slightly worse is the fact that Kataang is, in fact, a fulfillment of a fantasy, as said by Bryke themselves:
There's nothing wrong with putting your fantasies in your writing, of course, but Kataang is written from Aang's point of view, centered on Aang, and that's backed up both by the show and out of show materials.
Especially for a lot of Katara fans who don't relate to that dynamic, Zutara often felt more Katara-centered, or at least equally centered on both. Of course, that's a far more subjective thing, given that there's no textual Zutara in canon, and it's more of a fandom thing, but because it's a fandom thing, they can make it that way.
Also related to that critique of Kataang is the criticism of the finale and its weak points, especially in how Aang wins largely through the power of the Lion Turtle and a convenient rock. This feels especially strange when there was a previously set up way for Aang to reach the Avatar state, involving letting go of his attachment to Katara, which is portrayed as replacing his love for his entire people in The Guru. Especially right after his attachment to her is shown to lead to him forcing a kiss on her and acting possessive (nodding when the play refers to Katara as 'The Avatar's Girl'), it feels especially strange to Zutara shippers that this plot point from the end of Season 2 is never fully addressed.
In fact, a lot of Zutara shippers that I know actually feel that Aang was robbed of the opportunity to have a proper arc in some ways, and especially because of the bad blood with Bryke and Michael's documented habit of relating heavily to Aang (self-admittedly modeling Aang's adult design after himself and using an Aang and Katara cake topper at his wedding), blame Bryke for Aang's lacking arc, feeling that they were so concerned with giving him a happy ending where Aang got the girl that they caused problems for the story itself.
Personally, I do think that it's plausible that that's what happened to a degree, but obviously it's hard to know for sure.
Point 4: The Legend of Korra
Now, this might seem a bit strange to you, having watched Legend of Korra first, but Legend of Korra definitely didn't help with any of the critiques of Katara's or Kataang's writing by Zutara shippers. Katara ends up as the one member of the Gaang who doesn't have a statue anywhere, she's a sad old woman whose grandkid doesn't even recognize her, unlike both Toph and Zuko (the latter of whom is older than her!) she doesn't fight at all, and her family with Aang clearly wasn't a super happy one, given the bitterness Kya and Bumi hold against Tenzin, and the fact that Bumi didn't even think Aang was proud of him until he finally became an airbender. She wasn't even at her own granddaughter's air mastery ceremony!
Even her most famed accomplishments in Legend of Korra mostly fall by the wayside. She supposedly outlawed blood bending, but as the only other blood bender she wasn't even present for Yakone's trial. She's the greatest healer in the world, which is cool, but it's mostly used as a way to worf her and say that something is a problem even she can't solve. It's especially weird for someone who has the iconic line "I don't want to heal, I want to fight!" (while in-universe, it's possible to say that she changed, that change to have her focus on healing instead of fighting was a deliberate one by the writers).
Now, notably, a lot of the old writers on ATLA weren't there for LoK, and Bryke took over writing to some degree. Because of this, a lot of Zutara shippers, already more skeptical of Bryke, blamed them for how Katara was being treated. Again, it's hard to know if this is true.
Honestly, most people dislike the comics, and although they are overseen by Bryke, I don't think they're worth going into. Katara is mischaracterized especially badly, but in general everyone is mischaracterized so I don't really care enough to go into it. If you want to read more about the critiques of Katara in LoK and the comics, feel free to read Araeph's 'Consumed by Destiny' series of metas.
Point 5: What is toxicity, anyways?
Because of all of the above, and the fact that Zutara shippers frequently critique Aang's character arc or the show and think that it could have been done better or it had failings, they're often called toxic. People also claim that Zutara shippers are attacking a genocide survivor (referring to Aang, a fictional character) by being critical of his writing, or that Zutara is a colonizer x colonized ship and thus it's morally wrong for that reason, or something else.
On the other hand, Zutara shippers also call Kataang shippers toxic. Sometimes, admittedly, it's attacking them over shipping something which Zutara shippers view as a babysitter fantasy, but by and large (and I'm basing this off something that someone who ships neither said, though I can't find the original tumblr post), Zutara shippers tend to find the ways in which Kataang shippers behave toxic.
For example, it's pretty common that under properly tagged Zutara posts, you get people commenting about how Kataang (or sometimes Zukka) is better, or you get people deliberately mistagging Kataang posts as #zutara just to force Zutara shippers to see them. There's a lot of harassment campaigns that happen against Zutara shippers, with the most recent one being lead by someone called zutaraanti, who would take screenshots of properly tagged zutara posts and share them with her followers to make fun of, and would encourage harassment, ie, retweeting things like this on twitter:
Again, it's absolutely possible that I'm in a bubble to an extent, but I very rarely see a zutara post that's incorrectly tagged #kata*ng, and when I do, I normally also see Zutara people in the comments saying to fix it. I've seen it occasionally with Kataang shippers policing their own, but it's rarer in my experience, and I'm also used to seeing a lot of bad faith attacks like the whole 'colonizer x colonized' thing (especially funny when it's people who are fine with Zukka, Jinko, and so on).
Ultimately, both sides call each other toxic, but I do think it's true that what Kataang shippers and anti-Zutara people call toxic in general is criticism of the show and not being nice to characters like Aang (there are definitely some Zutara shippers who actively dislike him in general), while Zutara shippers consider harassment as the main thing which makes someone toxic, it doesn't matter what they ship as long as they do it in peace.
Point 6: Some additional points
Going back to your original ask, I'll be honest, I've never seen people on the Zutara end of things claiming that Katara is predatory in Kataang. Most of the critiques of Kataang in Zutara spaces end up being laid on Aang's head because of the non-con kiss.
I'm also not sure what's being referred to by 'denying canon'. If you mean shipping Zutara at all, then yeah, that's what shipping is, but that seems unlikely. If you mean the fact that Zutara shippers often think the canon ship was narratively a mistake, that's true, but surely this isn't the first time you've run into that? Not really sure what you mean.
As for "saying that the creators of a show are deliberately doing a āfuck youā towards fans of zutara just bc they didnāt interact much compared to the canon couple", well, I'm not sure I'd say that in terms of the lack of interaction. I do think it's important to remember that Katara and Zuko were absolutely very close by the end of the actual show, with Zuko confiding in Katara and vice-versa, but sure, it makes sense the canon couple would have more interactions.
I do think, however, that there is absolutely a deliberate "fuck you" to Zutara shippers? There's a bit where the Gaang are in the spirit world, and then Zuko and Katara are old like in Legend of Korra and Aang and Toph and Sokka are all younger, and a random spirit thinks Katara and Zuko are together, and Aang jumps in front of them and says they're not.
Like I'm not sure how else that's meant to be read, if not as a 'take that' to Zutara. Especially since we know they do just bring up Zutara unprompted sometimes to shoot it down:
Like to be clear the question there was not about Zutara at all. No one mentioned Zutara, they were the ones who randomly brought it up to shut it down.
So yeah, I don't know if it was deliberate that they avoided Katara and Zuko interacting, but I'd say it's not impossible, and I don't think it's crazy for Zutara shippers to say that it was deliberate.
Like I said, I personally am not necessarily convinced (I just think that they weren't actually thinking about most of the characters other than Aang when working on the movie, which is why Sokka is so mischaracterized, and as a result none of the Gaang really interact with each other), but I get why some people would think it's deliberate, especially combined with the scene in the movie deliberately shutting Zutara down for no reason.
So, yeah, that's a Zutara shipper's perspective on the whole thing, and why it's such a big debate. Ultimately, in my opinion, it boils down to Bryke effectively declaring open season on Zutara shippers back in 2008, which made most of the fandom hostile to Zutara shippers but also made Zutara shippers dig in their heels harder. Everything stems from that, and I think that makes the most sense as an explanation, because it's something that sets it apart from other ship wars, the creators openly taking a stance against a fanon ship.
Obviously part of it is that Zutara is also a very compelling ship to a lot of people, but you're right that most of the time that's not enough to let ship wars get so vitriolic, so I can only ultimately think of the Book 4 incident as the cause. Everything else is just background and explanation for how the two sides have dug their heels in after the fact in different ways.
Sorry if this reply is probably a bit lengthier than you were expecting, and you're welcome to disagree wherever you want. In fact, you probably should hear from a Kataang shipper, I'm sure they'd have a different perspective. Nonetheless, I'd appreciate a reply or a reblog to at least to confirm you saw it, since I put a decent amount of effort into collating all these sources.
