I've always thought this argument, and no offense to you of course, was weak.
Idealism of the seperation of church and state aside, for both "sides" of the issue routinely rally under its banner. Whether is be lefties removing religious historical monuments from courtyards or those on the right who provide "faith" based funding for social programs.
The inexorable truth is that the government's endorsement of any marriage, whether it be heterosexual, or now homosexual has always had its religious base.
A wiser move would be remove the mention of marriage from civil unions, and leave it like that. This way the government neither endorses heterosexual nor homosexual unions and leaves it to the wacky ethical playgroups which reside in the Churches, Mosques, Synagogues, Temples, Jedi Training Centres and Covens of our country.
On a day to day basis, does it affect me?
Hardly, but it does revive some of the old Kids in the Hall sketches!