Gotta respect the ingenuity at play here. Once they've gotten the point across that marriage is about much more than procreation, then they go after the idea of 'the sanctity of marriage'. Of course 'sanctity' is defined as 'the quality of being holy'. Once you have the state determining what is 'holy' and what isn't it is squarely in religious territory, which according the the doctrine of seperation of chruch and state is unconstitutional.
correct contemplator- that's exactly their argument- that if folks don't have children in three years, then it would be illegal to dissallow gays marriage because they contend that marriage is based solely on procreation - but htis is a lie. As you pointed out, it is about the sanctity, and htis is another key area that the gay folk are attacking as well.
But as one poster also pointed out, there is another issue they will have to overcome- the fact that children are much better off with a mom and pop- and this is fact. There may be soem exceptions of kids that do ok in two pop or mom families, but the research is overwhelming that it is NOT a healthy environment for kids.
This speration of church and state argument though is going to be the kicker in all this- I guess it could be argued that judges are set up by God and so must rule judiciously in a moral manner- not sure how that would play out though in court.