Actually it causes tonnes of problems.
My mother’s parents came from a little peasant village in Western Ukraine. I inherited her eyes, both the colour – an unusual shade of dark green, which I like – and the extreme near-sightedness, which I don’t. Before I had laser surgery (yes, it’s expensive and maybe dodgy, although it worked very well for me. I wouldn’t have gotten it if I hadn’t been really near-sighted) some years ago the non-contact-lens-filtered world was an indecipherable blur. So far I haven’t experienced the retinal detachment which nearly blinded Mommy Dearest in University. (Her roommate finally dragged her to the optometrist after listening for days to complaints about the annoying black screen descending steadily over her field of vision. She’s nuts, obviously.)
She once told me that some relative/ancestor of hers in Ukraine had married someone from “away”. That meant the village 10 miles off. I have no doubt that her weird eyes are the result of inbreeding. But that sort of gene-pool-shallowness, very common throughout history, is the result of geographical isolation and morbid hillbillyish dislike of outsiders. Islamic inbreeding is deliberate, systematic and religiously sanctioned. Pakistanis in Bradford don’t reproduce with their cousins because there’s nobody else around: they fly their underage daughter 4,000 miles back to Pak to marry some cousin (whose parents were cousins, whose parents were also cousins, whose own parents in turn etc. etc.) she’s never met. And it’s a huge problem which deserves a great deal of attention. Good luck with that.