May I ask why you don't like James Potter? Genuinely just trying to understand... Of course everyone is entitled to their own opinions, and you obviously do not have to like a character, but it just seems like you really don't like James and I can't seem to comprehend why...
In answering this, I'm sort of breaking my self-imposed rule of not openly discussing characters and ships I dislike. I'm of the mindset that because it's not hurting anyone, there is really no reason why fandom discourse should happen, and so many of the complaints I see people post/start problems with are things that I'd have rattled off to my mutuals and kept my general opinions to myself.
However, since you asked, I'll open the discussion.
First, I want to make it clear that I don't agree with most fanon characterizations. There's a reason I tend to stay away from some of the more popular fics, read primarily fics written by my mutuals, and use a very specific set of tags when searching on AO3. Don't take this as an attack on people who enjoy the fanon characterizations of everyone or as me trying to start something. I'm not afraid of the block button and, at the end of the day, I believe it is your (general) responsibility to curate your online experience, so if you see something you don't like on my blog or on anyone else's, I kindly ask that you block or unfollow and move on with your day.
It's not James as a character that I have a problem with, but rather his fanon characterization. Now, I acknowledge that everyone is entitled to their own opinions on this subject, but the "sunshine boy, golden retriever boyfriend, friend to all" characterization that seems to have been widely accepted by this fandom just has never sat right with me. I've talked about this briefly before (as a more general concept), but there does seem to be the idea that one's favorite character has to have the same morals and beliefs that they do, and often, in doing so, the character is stripped of a lot of their most interesting qualities/flaws.
Canonically, James is a much more complicated character and is someone who was, at times, arrogant, reckless, and cruel, especially in his teenage years. The fact that he publicly sexually assaulted one of his classmates in front of so many others, and that he ignored Lily's lack of interest for years, is glossed over a lot in fanon, and I personally find it uncomfortable to see that kind of behavior erased or minimized, and then replaced with this almost flawless, endlessly charming persona. It feels to me that in an attempt to make him more appealing or to fit certain ship dynamics, a lot of writers sand off the edges that actually make James interesting.
To be clear, I also recognize that people do this with most characters, not just James, so this, as I've already stated, is in no way an attack on any of those writers. I've found even myself doing this in some of my earlier writings, so I'm not innocent in this debate either. But with James, there seems to be a particular insistence on portraying him as a universally beloved, morally upright guy, and that just doesn't resonate with me. It's not that I think people shouldn't enjoy these portrayals, but it's just not what I look for in fanworks (or traditionally published media), and it's one of the reasons I've always found myself gravitating toward more nuanced or villainous characters. Barty and Evan are canonically absolutely terrible people, and that complexity is what draws me to them. In my experience, they're the only characters (and by extension, ship) that people allow to be morally grey or even downright evil, and it's only because of this dynamic that I still engage with the fandom. I don't need a character to be "good" or universally likeable to be interesting, and I find rough edges, moral ambiguity, and significant character flaws far more compelling.
Honestly, my issue is less with James himself and more with how the fandom (in general) tends to flatten characters into simplified archetypes (especially so many of the women, but that's a post for another time). I think we collectively lose so much when we decide that every character has to be sanitized to fit a particular mold. It's okay for characters to be flawed and messy. That's what makes fiction interesting!
So yeah, that's the gist of it. I don't necessarily hate James, but rather the way he's portrayed in fanon, which has ultimately colored the way I engage with both the character and the fandom at large. I hope this explains where I'm coming from!