Let me make this clear. A lot of you are missing the point.

If you support trans rights and you support someones identity, but you maybe don't support a trans billionaire as mentioned by one commenter, then that's but "I support trans people, but". That's just supporting trans people.

If your support for someones identity or rights is conditional then that would be the problem. Phrases like the one in the comic is often made when saying something controversial and invalidating, like only supporting some trans people or thinking it's okay to misgender certain trans people.