This discussion is regarding LBGTQ. Pedophilia, beastialty, objectophilia, looners, plushys and whatever else people are into are all of an entire different conversation.
Overindulgance of sexual activity leads to perversion. Perverted sexual activity, be it hetero, homo, masturbation etc. is the opposite of love. Therefore it's an addiction and ill.
I will make the boldest claim. Sex for reproduction is perversion/mental illness, it is just that the non-perverted did not reproduce so we failed to realize it.
I believe it applies to anything in life. You lose control over a certain aspect of your behavior, it serves you ill. It's a slippery slope that isn't easy to spot when you are on it.