People don't stop being trans because you disagree with them politically. I despise Jenner and other high profile trans grifters but I'm not shitty enough to deny their identities.
Do better. As a user of both sites this shit is genuinely upsetting. Despite how you may feel about hexbear, how can you claim that they bait people into revealing their internalized transphobia and then turn around and make shitty claims like this? I don't give a shit if you call me a tankie or red fash or whatever, but I'm trans whether you like me or not.
I agree, even if someone is a horrible person gender identity isn't something that should ever undermined or invalidated. Gender identity and sexuality are things you don't try to undermine or make fun of, no matter how awful of a person they are, because it sets a precedent for justifying that awful practice.
If we want gender identity to be seen as valid, it should be seen as unacceptable in all cases to invalidate it.
Hexbear users are assholes, and some of them may even push for things harmful to trans and gender-diverse people, but they still are the gender they identify as, and that should be acknowledged and respected, even if you don't respect them as a person and/or they aren't respectable because disrespecting gender identity indirectly hurts many other people, not just them.