[Vigilanteman]

Common is relative. It was not uncommon in early America either. One of my four great grandmothers was a product of a first cousin marriage. Her Mom and Dad met in early 19th century Vermont in an isolated community where there were just not that many choices. Her son (my grandfather) was a Cornell graduate back in the days where an Ivy League degree actually meant something. She was a brilliant lady as were most of her grandchildren (a number of college professors, an army general and other well accomplished people among them).

The problem isn't an occasional first cousin marriage here and there. It is still legal in many states, not including West Virginia. The problem is this type of marriage generation after generation, which is pretty much confined to Islamic cultures only.

[MarMema]

Pretty much but not entirely.
The largest issue are the recessive diseases that emerge. Too bad the Muslim world has not seen more of this.