The argument is that once we make marriage mean everything, it will mean nothing.<quoted text>
Protecting? I don’t understand, homosexual marriage does not attack heterosexual marriage in any way at all. There are over 18,0000 legal homosexual marriages in California now, It certainly did not hurt my marriage, how did it hurt yours?
It is a valid argument until you consider that who marries who is self limiting. There just won't be that many gay, poly or incestuous marriages to cause that problem.
Poly and incest marriages won't hurt your marriage either.