Re consanguinity (cousin-marriage): Approx. 26 U.S. States allow it; about 24 outlaw it. I once worked for the Kentucky Dept. of Natural Resources in Eastern Kentucky, where there were hollers in which the genetic negatives to consanguinity were evident. It's a coincidence that today in class I read to my students, for a few moments of levity, funny State mottoes, concerning which Kentucky's (from where I hail) is "Three million people; 15 surnames!" That's cruel!
Internationally, historically, there have been many societies that have or still do practice some form of consanguinity. The best known, of course, are Arabic societies, such as Iraq, who practice a patrilineal, parallel form of consanguinity. This more radical practice means that the preferred marriage partner is not only a first or second cousin, but also one from within the clan (endogamy and thus "parallel").
The other form is cross-cousin consanguinity in which the cousin issues from the parent who is exogamic, i.e., comes from outside the clan. In Arabic societies, the outsider partner is, of course, the woman (since Arabic societies are patrilineal). So, the preferred marriage partner is the child of the paternal uncle, thus maintaining the endogamous ties.
Just this week I asked a student in my class whether her Jordanian parents were cousins. My student knew nothing about cousin-marriage. Her parents' answer was an emphatic "no."
Incidentally, the endogamous cousin-marriage situation in Iraq is said to be a major hindrance to the workings of democracy, because of loyalty issues.