I would encourage Prager, and everyone else, to split the subject into 3 (maybe 4) distinct questions:
1) Should society tolerate romantic same-sex cohabitation?
2) Should same-sex cohabitants be able to share property, list each other in their wills, and generally create all of the various contractual relationships that are typically associated with marriage.
2a) Should same-sex cohabitants be able to raise children from previous relationships, from adoption, or from artificial insemination?
3) Should same-sex cohabitants enjoy the benefits that society provides thru legislation and taxation to marriage partners? i.e. should the family and medical leave act apply to same sex cohabitants, social security checks, etc?