Once marriage becomes a civil right we have more to worry about than same sex marriage.
Marriage is at best a qualified privilege.
It is not marriage that is a civil right. It is the equal treatment under the law which is a right. If, BY LAW, you give cash and prizes to some people who get married, you cannot deny, BY LAW, other people who get married from the same cash and prizes, unless (since some slippery slope people need the obvious stated out loud) such a marriage is harmful.
If the government stopped giving out cash and prizes to married people, we would not even be having this discussion.
But THE PEOPLE have been accepting cash and prizes from THE STATE for a very long time now. They have put those cash and prizes into THE LAW.
Therefore, THE STATE cannot "deny to any person within its jurisdiction the equal protection of THE LAWS."