There are people here and elsewhere in the TG community who, when they hear someone say gender identity is not a mental disorder, will tell you you're wrong. And some will fight you tooth and nail insisting they absolutely suffer from a mental disorder and that GID must remain in the DSM.
Going back to about the time homosexuality was still in the DSM, I recall what the general self perception of homosexuals was. And I think it's safe to say that back then you could have easily found many gays and lesbians who would insist they had a mental disorder and that homosexuality belonged in the DSM.
Go out in the G&L communities today and see how many gays & lesbians will say that now. I certainly don't know any myself. But I do know a lot who will tell you about the prejudice, bigotry, hatred and discrimination the G&L community faces. They recognize the disorder isn't theirs but rather, belongs to society.
Exactly what spurred their drive to come out, I don't know. But I'll bet once homosexuality was removed from the DSM and therapists and psychiatrists were no longer telling their clients, or anyone else for that matter, that gay is a mental disorder, it gave a lot of people a lot more courage to be themselves.
And once GID is out of the DSM, people like Mr. O'Brien will have to really dig hard to find a palatable spin to keep trans people out of society.