This is an empty argument because those who oppose gay marriage would not accept the assertion that it is demeaning. You could just as easily claim that allowing gay marriage is demeaning to heterosexuals. But let's pretend everyone agrees it is demeaning. Isn't it acceptable to demean someone (fines, imprisonment or other punishments) when someone makes some type of transgression? In the case of gay marriage, the moral transgression would clearly permit some of this.