My point is not that we should only ally with those whose "ideological purity is beyond reproach" - I too despair of this sort of idiocy.
But we should be wary of people who, though they seem to be pushing in the same direction as us, may go off piste in a dangerous direction after the legislation we approve of has been passed.
Never forget the three-way split:
TRAs: Interests and personality don't match biological sex? Modify your body to match your interests.
Fundamentalists: Interests and personality don't match biological sex? Modify your personality to match your sex.
Feminists: What do you mean, "your interests and personality don't match your biological sex?" Why on earth should they? You're fine just as you are.