It has to do with choices that are not natural. Natural is connected to evolution and natural selection, which, requires some form of sexual reproduction to pass forward genes. Gay willfully detaches from nature and natural selection since this behavior; male and male cannot reproduce. One needs heterosexual behavior to be part of natural selection.
Don't get me wrong, many gay men are nice people with a positive attitude that can be helpful to others. Many would be selected by nature for many reason, but their choice to detach, from the last step, which needs heterosexual connections, unselects themself.
What I always see as strange, is how Atheists believe in evolution, but they fail to teach natural selection in schools and show how certain human behavior breaks these natural guidelines. It is like they do not believe their own theory enough to use it for applied teaching. Then again the theory also uses dice and cards and games of chance, so any clear cut cause and effect may seem alien. This is not a moral judgement but rather a science based judgement for cataloging natural versus man made contrived.
In the 1980's, AIDS came around and plagued the gay community, more than all other demographics. AIDS and other STD's are still a problem that is disproportional for gays. This is because this detached behavior makes one more vulnerable unless you remain diligent and take manmade precautions to game the natural system.
Again, it comes back to evolution and science education that says one thing, but does not apply the theory to life experience and choices. It leaves the door open to do the opposite of natural and allow anyone to believe this is evolutionary. This is why I often think that science is not in charge of science. Science depends of others for resources; Government and Business, and the donors may have other agenda that are not science based; power and more money. Not preventing preventable disease can be a good business model if the goal is to sell drugs and other medical services.
Abortion is another from the same cloth. Pregnancy implies that the rules of natural selection have been followed; made new combined DNA, check. However, killing the unborn conflicts with an unspoken rule that birth and continued life of the offspring, are needed, just as much, or else we leave the path of evolution and natural selection. This is definitely part of a political and free market business model. The math is not hard to do. It is funny that religion can do the evolutionary math better than science, who stops short, due to quid pro quo.