Too long, I know.
I used to be against gay marriage. I grew up in a conservative household, where I was taught that homosexuality was a choice, an abomination in the eyes of God, unnatural, etc. I was still againt gay marriage into adulthood - I hadn't heard anything or met anyone compelling enough to make me reconsider my position. I'm a heterosexual man, happily married to a beautiful woman. One of my wife's bridesmaids was her sister, who is gay. My wife's sister and her partner have been together, faithful and happy for over seven years now. During those seven years, I have known heterosexual couples who have done everything there is to do to destroy "the sanctity of marriage" - adultery, divorce, rampant lying, inattentive or wholly abusive parenting, etc. My sister-in-law and her partner remain faithful to one another, take care of their nieces and their nephews, and love each other and the rest of the family purely and unconditionally. They were there on my wedding day, sharing in the celebration, wishing us well, letting us know they would be there for us as family for the rest of our lives. I would like to be there at their wedding day to do the same. In my mind, no two people deserve to be married more than they do. In my mind, no two people would better represent what it means to be married than they would. I simply haven't heard anything remotely approaching a justification for looking them in the eye and telling them "You can't be married. You can't have a wedding. You don't deserve the same recognition, by cultural definition AND under the law, that any two heterosexual people (who are qualified to be married only in that they are of legal age, can sign their name and pay a licensing fee) deserve."