"There's no principled reason why Gay marriage/adoption should be allowed that doesn't apply to polygamy/polyamory as well--- that same sex marriages are between two people and the others are between more is simply to describe them, not to give a reason why they should be treated differently."
You are right, though I doubt polyamory would take the nation by storm if it were legal. The right thing is for the government to get out of the marriage business altogether. Inheritance, custodial, and benefits issues can all be easily adapted to the very small changes that would result. Contract law is a very mature field, afterall.
I think it might have been better had the government never gotten involved in marriage... However, I worry that the family under such an arrangement would dissolve even more so.
In many of the schools I was a sub in, the number of kids without fathers was pretty enormous, and it had a huge effect on their behavior.
On another note, I can't believe Kristol is still attacking Social Security privatization! I know he and his father love FDR and don't care for small government or Hayek-style economics, but this is insane!