The purpose of all society, not just marriage, is to socialize children. If society didn't socialize children, then there would be no society. Marriage has long served as an institution for which children aspire. That is one major way in which marriage socializes children. But that is an extraordinary argument for same sex marriage. Believe it or not, there are gay children, and they want to aspire to an institution. Aspiring to second class civil unions and domestic partnerships is not the same for them as aspiring to same sex marriage. Seeing same sex couples in a committed, marital relationships would do much to socialize gay kids away from promiscuity and towards committed, long term relationships that would benefit them and society.