I think you'd agree that atheism and being gay are totally different because you choose to be an atheist and being gay is who you are and how you were born. You can't change that and you shouldn't be asked to change that to remain ...He says that as if it is an obvious truism, but leading atheists argue otherwise. For exxample, a popular atheism web site explains:
Do People Choose to be Atheists? ...Leading New Atheist Sam Harris wrote a book on how it is not a choice. Richard Dawkins refuses to say, and gives conflicting views here and here.
Personally, I tend very strongly towards involuntarism. I try to explain to evangelists that I do not in fact “choose” atheism. Instead, atheism is the only possible position I can have given my present state of knowledge. I can no more “choose” to just believe in the existence of a god than I can “choose” to just believe that the computer on my desk doesn’t exist.
Other prominent atheists also deny that it is a choice.
On the other hand, there is no proof that being gay is inborn or unchangeable. Here is the latest attempt:
The Bailey paper claims to have found large segments of chromosomes containing hundreds of genes that are common in gay men. The researchers admitted they couldn’t find any specific “gay genes.”For a survey of the evidence, see Biology and sexual orientation.
Last year, a paper in a relatively obscure journal also caused a public stir for saying just the opposite.
If you don't believe that something like religion or atheism could be heritable, see this recent book review:
Perhaps the main reason that scientists don’t think these psychological and attentional differences simply reflect learned behaviors — or the influence of cultural assumptions — is the genetic research. As Hibbing et al. explain, the evidence suggests that around 40 percent of the variation in political beliefs is ultimately rooted in DNA. The studies that form the basis for this conclusion use a simple but powerful paradigm: they examine the differences between pairs of monozygotic (“identical”) twins and pairs of dizygotic (“fraternal”) twins when it comes to political views. Again and again, the identical twins, who share 100 percent of their DNA, also share much more of their politics.