Andree Seu offers a good point: the push for bigamy is perfectly logical next since the needs of a bisexual aren't met by being married to one person of either gender. The only thing to stand in its way would be the reality that gay marriage alone will probably be enough to reduce marriage to irrelevance.
On a lighter note, another Chesterton quote I had to post:
"The woman has a fixed and very well founded idea that if she does not insist on good manners nobody else will. Babies are not always strong on the point of dignity, and grown-up men are quite unpresentable."
Yup. This means you, DOB. ;-)