Marrigae is a Christian institution, and the bible says a Man and a Woman. Having the gov go in and redefining it IMO is wrong. If gays sought an union equal to marriage, that's fine. But don't redefine something established by Christianity and force all the Christians to accept the new definition.
Besides, to me, it seems like changing the definition of a religious institution goes against a supreme court ruling in 1971, in the case of
Lemon vs. Kurtzman In the lemon test established by the ruling: (cut and paste from link)
The government's action must not promote a particular religion or religious view;
The government's action must not have the primary effect of either advancing or inhibiting religion; and
The government's action must not result in an "excessive entanglement" of the government and religion.
It seems like it may violate the third rule, to me anyhow. Maybe a violation of the second rule as well. Anyone else agree?