Lots of stuff that goes on in bedrooms is caused by mental disorders: child molestation, incest, rape, beastiality, etc. Homosexuality is one of them. The fact that homosexuals put political pressure on the psychology profession to take their personality disorder out of the DSM doesn't change the objective scientific fact that homosexuality is a personality disorder.
Incest, rape, and beastiality are not mental disorders - they are crimes. Committing an act isn't what a mental disorder is. Committing an act COULD be a symptom of a mental disorder but not necessarily. Someone could commit those crimes but not have an actual disorder. That isn't how disorders are defined.
You're right that crimes are not the same as disorders. But the fact is, mentally and emotionally healthy people do not engage in deviant or abusive sexual behavior. For example, the vast majority of child molesters were sexually molested when they were children. We don't know what causes homosexuality, but there is no such thing as a normal person, who "just happens to be homosexual." Homosexuality comes with it a host of other mental and emotional problems. For example, homosexuals are more likely to suffer depression, anxiety, have substance abuse problems, and are more likely to self-harm and commit suicide, than heterosexuals.
Higher Risk of Mental Health Problems for Homosexuals | Psych Central
Also, homosexuals are 10% less likely to report that they are "fairly happy" or "very happy" than heterosexuals.
Now, you're going to say that all these problems homosexuals experience are linked to society's non-acceptance of them, but I don't think that covers all your bases. Homosexuals now have won societal acceptance on many levels, and can now even marry one another, but all these mental and emotional problems have not gone away. Prior to the DSM being purged for political reasons, psychologists recognized that homosexual sexual orientation was merely a symptom of a much larger problem, which is a disordered personality on many levels. Now that the psychological profession has been terrorized into silence, they can no longer treat these problems, but must pretend homosexuals are "healthy" and that the only problem is societal disapproval. Not only is this an unscientific approach, it is harmful, because homosexuals really need psychological help, and they are not getting it.