I think gay marriage makes more sense to strengthen the modern idea of marriage... you know, getting married and raising a family.
First of all, gay parents don't have kids by accident. They have kids when they sit down and decide to adopt or get IVF treatment. It needs a lot of thought because it is hard to raise kids in a society such as today, as well as the responsibilities of being a parent. And as such, they do all they can to take care of their kids, rather than giving birth to Mr Jimmy Accident and raising a shithead of a child, all because they weren't ready to have the child.
Second, I'm not sure if they've noticed, but their idea of the nuclear family and modern marriage has gone down the toilet. The high divorce rates, single parents, broken homes... I don't think people will follow their ideas of marriage even if they were forced to. Now I know several gay couples who haven't married (one couple had a commitment ceremony, that's all) but have still lived together for fifteen years or more. And that's without some bullshit symbolism saying that they should stay together 'cause some skydaddy said it was a nice idea.
Third, there is no agenda. I've been gay for a while now and so far, my gay friends haven't called to say that we have a meeting to further some gay agenda. Sure, there's been pride parades, rallies and protests, but that's because we want the same rights you take for granted. It's just the same as if a rally of workers protested for rights in the workplace, or people protesting about the environment. We feel like it's a violation and an error of today that needs to be fixed, that's all.
But in my opinion, keep your damn marriage. It's all a joke to me.