Arguing that God is against gay marriage is different than arguing that the Constitution supports God's position. As to the former, the Church and its members can preach what they want--under the rights the Constitution affords. Whether they should is another queation. But as to the latter, I'm not sure what there is to gain in making that argument. I'm no Constitutional scholar but based on what I think I understand, the gay marriage constitutional analysis is pretty straightforward and the legal outcome was/is a practical certainty. Bottom line: the Constitution makes it very difficult for government to treat one group of people different than another based on sexual orientation.