Why not Polygamy?

By now the news has spread everywhere about the United States Supreme Court's ruling on same sex marriage. The dust is starting to settle, but I want to kick it up again. What now? Not only for gay rights, but what now for marriage? Is marriage now a beacon of equality or is it still an exclusive club only for some, only now same-sex couples have entrance? Specifically, what about polygamy?

It's interesting that many liberals have been ecstatic about same-sex marriage being passed; but if I were to ask them about polygamy, they would instantly turn around and condemn opening up marriage to such relationships. This is not to say that gay marriage and polygamy are the same. They are different and there are different considerations required for each. Yet, even liberals use the same arguments used to oppose gay marriage against polygamy as if they would somehow be successful for one and not the other.

Why not polygamy? The arguments against it are pretty standard, but let's go through them one at a time.

What's Wrong With Being Poly? Nothing!

In modern Western society, we've seen a great emphasis placed on marriage. Lately, with all the talk surrounding the marriage equality movement, it has become a very divisive issue in the public consciousness. In engaging in the ongoing public debate, an extremely common argument made is that allowing same sex couples would lead to all sorts of things like people marrying objects or people marrying animals OR people marrying more than one person.

So the first two make absolutely no sense whatsoever, as neither objects nor animals can consent so...that is really a non-issue. Despite this whole argument being a "slippery slope" fallacy, I would like to take this opportunity to challenge our boundaries on the third.