Actually, Arabs have been marrying their paternal first cousins for more than 1500 years, even before they became Muslims. And the custom has spread where Muslims have conquered, as in Pakistan.
There was an article posted here a month or two ago on this custom. One effect certainly is inbreeding. Another is the reinforcement of tribalism.
Maybe that helps to explain why so many of them are blood-thirsty nutjobs wearing towels on their heads. Yet another reason to banish them all from the West and make them return to their ancestral and natal hell holes to live.