Homosexuality is either wrong, or it is. It is either moral, or it is not. There are no in betweens. They know that, and it is about time everyone else admitted it also.
Who benefits from stable, monogamous relationships?
I think both society at large and the couple themselves benefit. Because of those societal benefits I'm happy to see gay couple given my implicit qualified approval in the form of civil unions. In the end though, gay couples are getting a greater benefit from their stability than society is.
Stable heterosexual couples bring greater societal benefits through child-rearing. That role deserves and justifies unqualified approval in the form of legal marriage.
"I disapprove of what they do, but approve of the way they do it."