Cousin marriage is only one of the problems; it has been allowed in non-Islamic cultures at various times, particularly in Protestant cultures (on the other hand, you had to get a dispensation in the Catholic Church because the general rule was that a first cousin was out of the running).
The other problem is polygamy, which does bad things to the gene-pool because you have a large local concentration of people with the same father. He, in turn, has at least some wives who are probably closely related to him because of the effect of not prohibiting cousin marriage and permitting polygamy.
The Jews, like all other primitive peoples, were polygamous, and God essentially brought them to monogamy. The Greeks and the Romans also abandoned polygamy, and one of the great strengths of Western culture was probably the establishment of monogamy, which meant not only better conditions for women, but more dedication on the part of men to their offspring, more traceable inheritance routes, and better, albeit unconscious, genetic selection.
I think people often discount the “side-effects” of religious practice and law. Islam is a perfect example of how a false religion can poison its entire environment.
Oh, heavens, you got that right. Polygamy + cousin-marriage (even without the rest of the Koranic claptrap) is going to yield a society just fraught with family dysfunction.
Plus, I strongly support the Catholic canonical prohibition against consanguinity, and I am convinced it contributed to Europe’s social, moral, and genetic health.
My point was just that cousin-marriage is not a distinctinvely Islamic thing. In fact, patriarchal nomadic and subsistence-agriculture societies tend to be cousin-marriers, in part because it keeps the flocks and property undivided, and in the clan.
I am fully persuaded that Islam itself was nspired by a bodiless entity or entities not in subjection to the Lord God. Need I say more?