A lot of alcoholics and drug users also manage to function within the larger society; many without detection for years.And what about being gay prevents a person from being "functional" as a person? Does it stop you from waking up in the morning and going to work? Does it reduce your ability to be mobile, to detect the world around you? Does it prevent you from cooking dinner, washing your laundry, paying your bills?
But that doesn't negate the fact that they have a problem that need to be addressed with psychological therapy and other professional help.
Homos are no different in this respect.