A constitutional amendment to ban gay marriage would be fine if they could do it without monkeying with the other amendments. But if the rats get a shot at the 2nd amendment they will try their best to change it so that only police and military have a right to bear arms.
It's been quite a while since I studied the procedure for amending the Constitution, but I think the alternative to holding a Constitutional Congress is to have 3/4 of the state legislatures ratify the amendment. I welcome any correction if I'm mistaken.