Since one of the main arguments gay marriage supporters use is, "You can't choose who you love," shouldn't this steer you away from marriage?
We've all ready got a divorce rate over 50% in this country---gay marriage supporters like to bring this up when people talk about the "sanctity of marriage"---so why would you want to talk about people not being able to control themselves? If you can't control your feelings, you're not ready to be married.
What happens when you take wedding vows, and then someone else comes along that you can't help but fall in love with? What happens is, you have to make a choice. Either you A) honor your commitment or B) you further denigrate marriage.
I'll be the first to admit that we have a lot of problems with this institution. We're shooting ourselves in the foot by what we teach our young people about love and sex. We don't help ourselves by telling singles that there's something wrong with them if they're not married by certain ages. And we've definitely screwed up by being accepting marriage as an "As long as it works," scenario instead of reinforcing the idea that it's a lifelong commitment. We don't need to compound our problems by perpetuating the idea that people can't control themselves, and that it's okay that they can't.