What do you think about gay marriage?

I challenge someone to give me a solid argument for why gay marriage should be banned. And please don't bring up all the religious bs because I've already heard it all and it never produces any kind of real argument. Sorry. I have absolutely nothing wrong with religion, I have some spiritual beliefs myself and I'm actually a very open-minded person.... I only want to know from a nonreligious standpoint how someone could successfully argue that we all don't deserve equal rights. I'm sorry for sounding defensive but I'm just so sick of hearing people talk about how its "God's will" and this and that. I'm trying to understand the "logic" behind a ban on gay marriage without having to listen to people babble on about religious nonsense on the matter. I want a real argument.