The only reasons anyone should need to support gay marriage are these:
"right is of no sex, and truth is of no color. God is the father of us all, and all are brethern."
and
"where a wrong is done to one man, it is done to all men."
Injustice for one is injustice for all, and I want to live in a country where everyone receives equal treatment under the law, regardless of how that hurts or helps me, personally.