It was an anti argument, but it fell apart when it became obvious that one of the main reasons people in same-sex couples wanted to marry was because they were raising children together.

There is a good reason why defense of marriage is the argument. If marriage is a voluntary contract between equals who choose each other, then same-sex marriage makes sense. If marriage is a holy mandate in which the female wife is subordinate to the male head of household to whom she is beholden for financial support, then same-sex marriage does not make sense. Allowing same-sex marriage puts a civil stamp on companionate marriage as a concept. Women in traditional marriages have a lot to gain from the legalization of same-sex marriage. People who think of this as defense of marriage may or may not realize what kind of marriage they're defending.