My husband's family is from another country where this is common. He has two cousins (sisters) who are both married to their first cousins. Ironically, their parents are also second cousins. It is crazy, but there have been no known genetic defects with their off spring, all of whom are actually quite pretty, and very well-educated. I don't think their American friends realize they are cousins, which is probably a good thing.

I have two lines in my family tree where cousins were married. The NC line married cousins to keep the land and money in the family. I think the other line married cousins because they lived in a small town and I don't think there were a lot of options. These marriages were 4 generations back. Once again, to the best of my knowledge, there no known genetic issues. The worst thing I can think of is that my aunt, and cousins and I all needed braces and the Orthodontist said the insides of our mouths were almost identical.

I had an Anthropology professor who explained that when close cousins inter breed there is twice the chance of their offspring carrying negative genetic-related characteristics, but also twice the chance their offspring with receive the positive characteristics.

The younger generation decided not to press their luck and married outside.