It isn't, and should be available to all gay couples
Being gay is wrong, so they can't get married
The sanctity of marriage. No, I wasn't laughing. I was coughing. *cough* ... see?
It will set a bad example for Christian youth
I don't honestly have a good reason, but I still say no
Other (please explain)
More to the point...you can't automatically assume that your neighbor's cow might be in love with you, wants to get married, and have Big Macs.
"A woman is like a teabag, you never know how strong she is until she gets in hot water." - Eleanor Roosevelt
Keep your religion out of other people's marriages.