Do you consider impotence a choice? If not, do you think the human race may possibly become extinct because we will all become impotent and be unable to reproduce?
Before I go further, I should clarify what I am
not saying. I am not saying that homosexuality and impotence come about in the same way, biologically. I am also not comparing them as a condition (as some might be tempted to think that since impotence is generally perceived as an affliction or a system flaw, that I am saying homosexuality is also an affliction or a flaw...something I do not believe at all).
The point is, you cannot use the simplistic logic of "If something does not directly aid in procreation, then clearly it is not naturally occurring because, you know, natural selection."
There are recessive genes. There are both heritable and non-heritable traits that emerge in a minority of the species. "Evolution" is a simple concept but an extremely complicated process in the natural world that takes actual study to speak knowledgeably about. You cannot simply apply it at whim in casual conversation.