Yes. Straights can marry so denying gays is an affront to civil liberties. Either banish straight marriage and only have state sanctioned civil unions for all or live up to the spirit of America and let gays marry.
I am straight, I am married, and I can say 100% that gay marriage does not threaten my marriage.
The only marriages it threatens are marriages where the homosexual Republican has been in the closet for 50 years.