Tell me. Why would people choose to be gay? There were plenty of people who got persecuted for being gay who were gay. So why would people have made a choice that might even get them killed. There are, in fact, gay people in Russia (where being gay is illegal). Why wouldn't they just choose not to be gay?
And what you said about kids not being gay from birth. In fact, studies have shown that people with a gay sibling are more likely to be gay.