Except that this is easily disproven by long-lasting gay male relationships where both participants are completely happy

. Also, the phrase “homosexual lifestyle” is highly offensive. Please do not use it. Please use “actively gay” or “actively homosexual.”
Except that this is easily disproven by those who have no interest in sex, such as stone butch lesbians

. Also, as someone who has had sex with someone of the same sex [before I was Catholic], it has nothing to do with “selfish sexual behavior” and is almost always aimed at keeping your partner happy, smiling, and at low stress levels. Sounds pretty selfless to me if we’re not allowed to bring up theological repercussions.
Because they don’t, at least not at higher rates than heterosexuals. So no, this wouldn’t explain anything.
Except lesbians have STD transmission far below that of straight people, so this argument would seem to endorse lesbian sex

.
The truth of the matter is there are very few and far between arguments against gay sex (as opposed to, say, gay marriage) that do not involve theological discussions. Most secular arguments people use are specious, based on faulty data, based on stereotypes, or just plain outright false. Literally the only one remotely convincing is the argument that there was a natural design for genitalia, but even then this necessitates a belief in God, or else there would be no repercussions for going against said natural design.
There is a reason that actively gay people literally laugh in the face of religious arguments that try to enter the secular world. I always marveled, when I was actively lesbian, how all these religious heterosexuals knew just exactly how and why us gays were having sex or even dating each other. Apparently they knew us so well that we were completely unaware of any of the horrible, sinister statistics [that don’t actually exist] involving LGBT people that they knew everything about, despite us being intensely immersed in the community and largely only having LGBT friends.
It is an insult to the intelligence of the LGBT community to tell them you know better than them as to why they are doing what they are doing. It is an insult to the intelligence of the LGBT community to tell them you know better than them as to what goes on in their community. Focus on arguments that are actually true, not on arguments that, despite being false, win brownie points among other religious conservatives.