A Little Cup of Cyanide

You know what I've never seen? A really strong argument against homosexuality that doesn't bring up God or the bible. I'm starting to think it's not possible. Christianity is a religion based on faith. So, let's say for a second that someone has proven that God isn't real. Is it safe to assume that everything written in the bible could be a lie as well? So, if marriage is a unity between a man and a woman according to God, but there were no God, would homosexuality be considered wrong anymore? Like I said, Christianity is based on faith that God is real and that you should live your life according to the bible. It's all based on faith. There isn't really anything concrete about it.

So, here's my challenge. Somebody give me a convincing argument against homosexuality without any reference to God or the bible. Anybody. If you're reading this post right now, and you think you can do it, please do. You won't change my mind or anything, but at least you'll have the satisfaction of proving me wrong.