In their minds, that is.
Our side considers legalizing same sex marriage to be a redefinition of marriage. We try to persuade people that redefining marriage would be harmful. But I have noticed that many people who favor ssm have ALREADY mentally redefined it. In their minds, marriage is only about adult relationships, with children as optional, for sure, and sometimes with permanence and fidelity as optional as well.
Since marriage is already just about adults, they can’t understand what the fuss is all about. Why not just include same sex couples in this more or less pointless vestigial social institution called marriage? They can’t understand why the legal system doesn’t catch up with the image of marriage they are already carrying around in their heads.
They don’t see that by continually defining marriage down, we are making marriage less and less able to perform its intended and necessary social function of attaching mothers and fathers to their children and to each other. And they don’t seem to see that having a functional next generation is in everyone’s interest.