It's not. That's why people are upset -- because all she cares about is self-interest while attempting to be representative of trans people.
Maybe should have made myself clearer. There is still plenty of posts in this thread basically saying "oh she's stupid, voting against her interests, don't she know that cruz hate trans people" and that's mostly the kind of posts i find a issue with as i think the argumentation in itself reduces minorities to a monolith.
I mean obviously a lot of people are making a valid point about her being a idiot for endorsing christian fundamentalists and being anti same-sex marriage while claiming to be a representative of trans people.
Basically my argument is that a lot of people seem to have a very idealized picture of how people classed in the same minority view one another. Like for example that people find it very offensive that a affluent, wellsettled latino would vote Trump or that affluent black man would vote for a racist politician. I.e. an assumption that a certain trait (skin pigment/sexual identity/religion etc) would trump all other aspects of a person.
Personally I would love people to act out of solidarity rather than self-interest but I doubt that white straight cis-men would get scrutinized over pursuing self-interests to the same extent as "uncle toms" (although the argument in this specific case about caitlyn claiming to be a representative for trans people kinda makes this last claim void in this specific case)