The other problem with DSM is that it's too normative. Homosexuality is a "disorder", but then when you start treating homosexuals nicely they suddenly become less traumatized, more come out, and you realize that most of them aren't as sick as you thought, and that a lot of the sick ones are like that because you marginalized them in the first place.
The concept of a mental illness is fundamentally normative. Even if you think homosexuality is perfectly OK, you need to admit that it was removed for purely political reasons. Objectively it is clearly abnormal: perhaps 1%, perhaps 3%, whatever... but TINY.
If you insist on adding the requirement that there be harm, and you want to dismiss the suicide issue as a trauma result, the situation is still pretty clear from numerous viewpoints. In the USA, AIDS is still primarily a homosexual disease. I can even argue this from an atheist viewpoint: if something prevents offspring in the Nth generation, impacting one's evolutionary fitness, then it causes harm. (and we all know what the typical Christian/Muslim/Jew would argue)
Given that we've already found brain differences, this new system seems like it can not avoid bringing back homosexuality as a medically accepted illness. This is not to say it can be treated or that any future treatment would be worthwhile, because the cure can be worse than the disease. Nearly nobody is going to risk surgical and/or genetic brain modification to become heterosexual. Almost certainly it would be considered unethical to even attempt such a risky modification.
BTW, there tend to be differences between the brains of republicans and democrats. Care to declare one of them in need of treatment? (sure, the other team!)