Bush, Kerry, and Nader Respond to Youth Voter Questions
If marriage is a religious covenant, and you believe in separation of state and religion, then marriage should neither be recognized nor accorded special status under the law.
But that is not the case. Married couples are give extra rights and privileges under both state and federal law. Therefore, it cannot be said that marriage is a strictly religious covenant (IE, marriage also exists as a legal institution). Which means that there is no basis for denying the same rights to gay and lesbian couples.
BTW. Get over it. If allowing gay couples to marry somehow demeans your own marriage, then your marriage sucks in the first place.