That's certainly true. But the genetic impact is only another thing that reveals that the problem with Islam is that it is evil at its core, destroys everything it touches and produces nothing good.
I think that there should be preaching in Christian churches on a daily basis that points out the difference between the truth of Christ (and the Christian vision of life, which frees and makes creative) and the falsity of Mohammed's evil fantasy cult (which enslaves, destroys and brings darkness).
Cousin marriage was legal throughout the USA until the 1860's, and is still legal -- sometimes with restriction, but mostly without restrictions--- in the majority of states. It is also legal throughout Canada and Mexico; in fact, the US is the only Western country that has any restrictions on cousin marriage at all.
So it's just factually wrong to see cousin-marriage is a distinctively Islamic thing, although Muslims (especially the Arab Muslims) do socially favor it to a high degree, whereas in the USA, even where legal, we tend to socially disfavor it.