Unfortunately, they’re not breeding themselves out of existence, simply into a progressively more dysfunctional and low-IQ condition. But their fertility rate seems to be the only thing unaffected by this.
Nature will find a way.
No, they are not breeding themselves out of existence. Think of our own stereotypes of Appalachia, which actually has some basis in fact. They (in)breed like rabbits and show signs of genetic defects. And some of the manifestations of those defects are lower intelligence and being prone to random violence.
The Clampetts were muslims at heart. And got their money from oil, too.