I can't see how insisting on the amazingness of heterosexual marriage is the best way to protect children and families across the board when such an approach excludes all the children of unmarried heterosexuals, not to mind the children of married or unmarried heterosexuals, single parents, orphans etc. You might as well reintroduce illegitimacy for children of unwed parents if you go down that road. These people are either homophobes-in-denial, complete ninnies, or both.
They are basically like the black knight in the Holy Grail. Every argue they had has been hacked off, and they're still trying to headbutt people.
Society is headed in one direction on this.