I do disagree about horseshoe theory. People being far-left vs far-right are similar only in that they passionately believe in radical politics. The actual views, however, are staunchly different.
I think you are missing my point. It is not their political views that are similar, but how they treat others in relation to their views.
Dehumanisation of opponents, antagonisation, false flags, discrimination, etc are all part of the playbooks for both the extreme left and extreme right. While the extreme right has racism, the extreme left does 'reverse racism' (basically another brand of racism). Same with gender, the extreme rights have misogynists and the extreme left has misandrists.
Remember we're talking about extremist circles here. Obviously in wider society, one side of the whole discrimination issue is a much bigger problem than the other to the point where it's practically disingenuous to compare the two.
The claim by the subject of the OP is that people on hexbear “white knight” trans identity and use it as a shield, despite being cis, on the grounds of being confrontational. This is a claim without evidence, just vibes.
This is true, I have no evidence. The only thing I've said is that I can believe it, and the reason I can believe it is that I used to run in alt-right circles in the past and have a friend that used to run in extreme left circles. Their playbooks and tactics are shockingly similar, and dishonest enough to the point where I would not be surprised if there was a contingent on Hexbear pretending to be trans in bad faith. It is entirely consistent with what alt-right trolls would do.
With that said, you are also correct in that we cannot just no-true-scotsman away the fact that there may actually be some trans people involved in these trolls. There is a lot going on for a lot of trans people in communities with little acceptance, and you may have some that are trying to project an image or are in outright denial to themselves, just like how some gay people were when homosexuality was the big taboo. Or heck, they may actually feel the way they say they do, and want to lash out against a society that didn't accept them. I certainly couldn't blame the latter group tbh.