Again, I submit that Brian's reaction was not to the simple fact that Quagmire's dad was trans, but rather because his sexual identity had been seriously violated and as a result he'd been psychologically traumatized.

See, this is what's very, very wrong about this situation: this "sexual identity had been seriously violated" thing. Why has his sexual identity been violated? It could only be violated because he believed that a transwoman is not a "real" woman. He believed that a transwoman is some sort of man in disguise, not a woman, and that the biology (and his own perception of her) is the truth and not how the person chooses to define herself. And that's sick and horrible and I have to refuse to think that this is the norm for white, cis-gendered men, because I would have to believe them even more damaged by the patriarchy than I already do.