The Gays Are My Friends

So i was taking my Religion class the other day, which incidentally is a complete bust, and somehow homosexualism came up. I'm not a homo, but I'm totally on their side. My teacher is a complete asshole when it comes to controversial subjects, he thinks he's always right, and he started blabbing on and on about how people cannot be born gay. This obviously pissed me off immediately because all my life I've been taught that people can TOO be born gay, and then again, some become gay because of their life experiences. I mean, if dogs and cats can be homosexuals (and I don't think they do that because they've learned to be that way or are "mentally ill" like some dare say), then why can't human beings also be born gay?? You tell me...