Sure there is. Marriage is about producing and raising children, that the society or state can continue.
I don't like kids, I guess I can't get hitched. :(
This is why I especially find "marriage = children" arguments are upsetting. I feel the logical conclusion is disallowing non-child producing marriages as well. I also think it's a pretty clinical way to look at a beautiful thing.
Maybe I'm just paranoid *tinfoil hat*.