From MeFi:

Dahlia Lithwick has an interesting article on Slate commenting on the real threats to marriage in light of Massachusetts Supreme Court's declaration that same-sex marriage is protected by the Constitution. Lithwick lists:
1. Divorce (~43-50% of all US marriages end in divorce)
2. Frivolous marriages (i.e. it is easier to get married than it is to drive a car, buy a gun, buy alcohol, etc.)
3. Birth control (is marriage "only for procreation"?)
4. The various challenges to our time and attention that take away from quality time with our spouses