Reworking the constitution

Correct me if I'm wrong but the US Constitution (or any state constitutions I'm aware of) have never been used to limit the rights of individuals. Read it. All of it's statements give rights, not limit them. Any sort of constitutional ammendment to ban something (i.e. gay marriage) would be setting on Hell of a nasty precident. Besides, how is a ban on gay marriage any different then bans on multi-racial marriage from the previous century?