It doesn't take much effort to learn what actual TERF, alt-right, tankie, or other online-hate-group rhetoric looks like, including the "dogwhistles," motte and bailey arguments, and other stuff they use to try to seem more innocuous they are and to make their hateful beliefs seem more "reasonable" to the not-yet-converted. I don't usually recommend people get their information from YouTube, but that's where some of the best informing about how online hate groups work is going on right now: specifically, I've recommended Innuendo Studios' "How to Radicalize a Normie"* a million times for talking about how hate groups recruit (with a specific focus on the alt-right); I also recommend his longer Alt-Right Playbook series as well as ContraPoints' "Decrypting the Alt-Right" video. ContraPoints' videos on "Gender Critical" and especially her recent "The Witch Trials of J.K. Rowling" are also good examinations of common TERF arguments. Here's an article on how the men's rights movement uses cult tactics to hook its followers; Contra also has a good relevant video on "Incels." As for tankies, just reading stuff by actual legitimate historians about the history of the Soviet Union (particularly the Holodomor) and Maoist China or whatever authoritarian regime they're trying to rehabilitate, is enough to counter their shit; Suki Kim's book Without You, There is No Us is a great exposé on what life in North Korea is actually like, from her having gone undercover in Pyongyang as a university professor. Suffice it to say she got to see a lot more than a couple of Australian boys who spent a few days there getting the regime-approved highlights tour and didn't question it.
But all this is to say is that being a generally informed and critically-thinking person, and also, familiarizing yourself with their actual arguments (which you don't have to do by reading their garbage, you can do with reading or watching investigative journalism about those movements, which all of the above are) is the best defense against this. It's much more effective than the Tumblr backwards-rock-lyrics approach of obsessing that you might somehow radicalize your followers by reblogging some unrelated post where the OP is a TERF (or w/e). Even with innocuous stuff that are actual symbols -- like the alt-right's emoji obsession -- those are more to signal to other members of their hate group than to radicalize you. An emoji of a glass of milk won't do anything to you if you aren't aware that it's saying something about race. Subliminal messaging is not a real thing.
But also just like... have more faith in yourselves? I found those videos above helpful for understanding how hate movements work, but I didn't need to watch any of them to know that racists and misogynists and transphobes are wrong. I think some people have taken the ideas of "in a racist/patriarchal/heteronormative/colonialist/etc. society, everyone buys into those ideologies at least somewhat" and "you are not immune to propaganda" as well as that even smart people can fall into times when they're lonely and vulnerable and groups like cults prey on that... and think that means they're completely vulnerable to any and every hateful group or person trying to recruit them. But in fact, not everyone is vulnerable; there's a reason that people who leave cults and extremist groups often hop to a new one, because they do attract particular personality types and repel others. You can do things to arm yourself against recruitment. The biggest one is just educating yourself: about the rhetoric of specific groups, about how extremist and high-control groups operate in general, and about general critical thinking skills (for example, by learning about lists of logical fallacies). The better-informed and more critically-thinking you are in general, the more skeptical you are of simple solutions for complex problems, and also the more compassionate you are, the stronger your core moral and political principles... the less vulnerable you'll be to extremists, hate groups and cults.
I've had feminist posts take off that resulted in some TERFs following me; there absolutely are some who think every cis feminist is fruit ripe for the picking. I never worry about this. A lot of them are obvious from their usernames and blog descriptions, so I block 'em. If they're not, they usually reveal themselves quickly with their attempt at "recruitment" via reblogging one of my posts with some nonsense barely-an-argument, and then I block. And if I don't ever catch them? ...Well, look, I've read shelves of actual feminist theory, I have a lot of trans and nonbinary friends both on- and offline I regularly talk to about gender and feminism, I follow news about trans rights closely and support trans activist campaigns, I'm familiar with TERF arguments and how to counter them. I feel pretty confident that no TERF is going to recruit me, especially a Tumblr rando. In fact, I feel just as confident that following someone like me -- a cis lesbian feminist who is well-informed on the rhetoric of their movement and where it leads them astray -- is much more likely to de-radicalize them instead, especially as I've noticed a lot of them are young and very uneducated about feminism. It still probably won't happen; as the videos I linked above illustrate, de-radicalization is really hard to do via social media arguments (and so I still try to block them whenever I find them, out of concern for the safety of trans and non-binary people I follow and who follow me). But it is an astronomically more likely outcome. That level of confident is where you've gotta be, and I think a lot of you are closer than you realize.
(*Note: Ignore YouTube's "viewer discretion" warning and age restrictions here; they're a result of racists mass-reporting the video. Do note Innuendo Studios' own card at the beginning about content warnings. But it's no more violent, graphic, etc. than any other video explaining hate group ideology. If you can handle the Contra videos or his other Alt-Right Playbook videos, you can handle this one.)
