I don't understand why christians in particular should have something to say about marriage?
My husband and I are atheists, and got married in a civil service at City Hall. We did it as a way of celebrating and solidifying our relationship. Is our marriage now a farce, because we didn't go to church - a church we both find oppressing and closed minded - and stood in front of a god we don't believe in?
And not having the right to take time off to take care of your spouse or being the next of kin in case of death, that's not small potatoes. It's not farcical to get married to obtain those rights. Marriage is an easy way to obtain those rights, it is also a cultural ritual well established in most, if not all, societies, so why shouldn't gays be let in on it?
And regarding the downfall of society... I think rather than gays getting married and going about their lives, we should worry about drugs, sexual trafficking, destruction of our environment and war.