So a chap in the States is kicking off about the fact he can't legally marry his second partner, his argument being that homosexuals got the right, why shouldn't he?

As we know Polygamy isn't a recent phenomenon, it's advocated by sum religions(obviously times being a hell of a lot different back then) so what's your view?

Have the countries that have legalised gay marriage opened the flood gates for things like this? Is equality truly for all or just a word we use for people who don't make up the vast majority?