(Serious) If society is allowing gay marriage, why not allow polygamy and marriage?

As far as polygamy, I see no reason to forbid it; if a bunch of people all love each other, it doesn't really matter. But I do have to agree with the other people who brought up the ual and bestial marriages. Cousin-Cousin ual is as close as should be legal (and even then you still run the risk of birth defects), and bestiality should still be illegal because an animal cannot give consent to marriage or .