Bestiality -easy. Animals can't sign contracts. Animals can't consent to sex with a human, therefore it's animal abuse.
This is a gender based. That's it. It violates equal protection because a man has the right to marry a woman, but a woman does not (and vice versa). To discriminate as such, the state is required to prove that harm would be caused to the state were the discrimination lifted. Considering 18,000 same-sex couples were already married in the state and harm could not be argued, it had to be overturned.
You are required by the Constitution to treat all citizens equally regardless of gender unless it is proven to be in the state's interest. Even if a majority thinks it's in their interest, that matters not. In the South (less so in the North), a majority thought that blacks and white shouldn't marry and passed laws that said so. The Supreme Court said that Virginia failed to show how such discrimination was necessary to preserve order in the state. It was therefore overturned.
This is no different. It does not open doors for polygamists. It does not open doors for pedophiles. It does not open doors for beastialists (is that word?). All of these restrictions are easy to prove where harm would occur to the state and its citizens were they to argue for marriage rights. This has been shown to you and other on multiple occasions.
It's really not that hard to figure out.
Those of you who are so adamantly against same-sex marriage will look to your grandchildren just as bad as the people who fought to keep people of different races from inter-marrying. You won't look noble. You will be viewed as either quaint or bigoted by future generations. It's your choice.