From the AP:

In her second day of testimony, Nancy Cott, a U.S. history professor and the author of a book on marriage as a public institution, disputed a statement by a defense lawyer that states have a compelling interest to restrict marriage to heterosexual couples for the sake of procreation.  Cott said marriage also serves an economic purpose – one that was especially pronounced when it was assumed that men and women performed different jobs in their partnership. But as traditional gender roles and the purposes of marriage have changed, the reasons to bar same-sex couples from marrying have gone away, she said. “It does seem to me that the direction of change leads consistently toward the appropriateness of allowing same-sex couples to marry,” she said. “There is no longer the expectation that the man-woman differentiated, need-bound household is needed.”

In that case, Dr. Cott, what exactly is the purpose of marriage? Sharing health insurance and making people feel good?  If so, why is that a public purpose at all?