The polls say that folks are supportive, now, but I think that they will get a belly full of the activists pushing themselves on every florist, caterer, bakery, church, etc. simply to make a political point. I foresee lawsuits against the Catholic Church, especially, since they don't like the Church's teaching against homosexuality, and they will try to force Catholic parishes to hold same sex 'marriages', or have their tax exempt status taken away.
I think Catholic Churches should stop doing the civil part of marriages entirely, and not be an agent of the State. They could do Sacramental Marriages ONLY, within the teachings of the Church, and that precludes same sex marriage.