"There's never an egg timer around when you need one." Joking aside, this is exactly why I oppose gay marriage. If you can change the definition of marriage (union of two willing adults of the opposite sex) to include same sex, why not change it to include more than two people? Why not change the requirement that one or both be adults? Or that they be willing? There's precedent in other cultures for all of the above. Next thing you know, you can "marry" an unwilling 9 year old girl, do whatever you want with her and then "divorce" her. No-fault, of course.
Or you can marry 6 illegal immigrants, making them legal and requiring your employer to provide health insurance (for which you might quietly charge a fee from each new spouse). Oh, the possibilities for wrecking our culture and our ecomony are endless.
Now, let's think. Who's been trying to wreck both since the early 20th century? Oh, well.. guess we should just MoveOn, cause there's no A.N.S.W.E.R. ... But dude, where's my culture?
You are throwing in children presumed not to be able to give consent in with what consenting adults do.
Why not just get government out of the business of regulating marriage? Why, for example, should anyone need a "marriage license?" Why not just have a registry of next-of-kin?
I wonder how old the practice of government marriage licenses is, and whether it is a hangover from miscegenation laws.