How Do We Feel About Cousins Getting Married?

Incest taboos came about, yes, because of higher instances of birth defects, etc, and the pre-science "explanation" of offense given to whatever local deity was worshipped. We have a better understanding of things now, and the ability to map ones genome. Laws like this only continue to make sense if you’re in favor of scanning the potential couple and barring reproductive rights (because marriage isn’t just about reproduction) to that couple if they cross a threshold of risk for "defective progeny".

Yes, this applies to marrying ones sibling as well. And yes, nearly anyone reading that, including myself, has a negative reaction to that, because we’ve all been conditioned to not regard sibling as potential mating partners, and there’s more than some evidence that’s baked into our genes, because many other animals also have naturally occurring incest taboos, likely due to the tendency to form family units amongst them.

http://onlinelibrary.wiley.com/doi/10.1525/aa.1963.65.2.02a00020/pdf

Kind of like gay marriage, it seems like something we made illegal because most of us wouldn’t want to do it and didn’t see the need for it. There’s been a huge political will to legalize gay marriage and it still took decades because of how that issue has come into the limelight recently. But gays are a relatively integrated part of society, whereas, well, I don’t know, when I imagine incest I’m usually thinking about the stereotypical redneck type family arrangement. Which probably makes it harder to stomach for the people more in the center of power.

I don’t buy the slippery slope argument for marriage, just because we legalized gay marriage doesn’t mean we’ll be legalizing polygamy tomorrow.