When it comes to cousins, it is definitely a cultural thing going back to biblical times, although the original reasoning you stated might be why it was that way.
My wife is Syrian and her parents are cousins. They come from a long line of Christians with no known conversion from Islam, so this isn't just a muslim thing. In modern times, it is considered normal in the Middle East for cousins to marry, even for Christians who don't believe in polygamy. I can see in their family, however, what I think are genetic defects due to marrying cousins and I think there is a lot of thst in thr Middle East. My understanding is this was somewhat normal in the US until backwoods types overdid it and shined a light on the genetic disadvantage of not pursuing a genetically different mate.
The trick is eligible women are rare and valued. Thus when looking for a wife you end up using the good old boy network to find a wife. So you end up talking to your family and people in your village and find a wife in the village next door. Well because of previous wife swaps that woman is your 2nd cousin. Its proximity plus familiarity. The fact that an eligible woman is a rare thing complicates matters and makes this type of thing more likely. They can't just go find a woman anywhere. They have to take whatever they can get.
The same with Christian communities. They can only marry other Christians. Thus their are fewer of them. Thus they end up eventually being with a distant relative. The mass exterminations etc don't help.
When it comes to cousins, it is definitely a cultural thing going back to biblical times, although the original reasoning you stated might be why it was that way.
My wife is Syrian and her parents are cousins. They come from a long line of Christians with no known conversion from Islam, so this isn't just a muslim thing. In modern times, it is considered normal in the Middle East for cousins to marry, even for Christians who don't believe in polygamy. I can see in their family, however, what I think are genetic defects due to marrying cousins and I think there is a lot of thst in thr Middle East. My understanding is this was somewhat normal in the US until backwoods types overdid it and shined a light on the genetic disadvantage of not pursuing a genetically different mate.
The trick is eligible women are rare and valued. Thus when looking for a wife you end up using the good old boy network to find a wife. So you end up talking to your family and people in your village and find a wife in the village next door. Well because of previous wife swaps that woman is your 2nd cousin. Its proximity plus familiarity. The fact that an eligible woman is a rare thing complicates matters and makes this type of thing more likely. They can't just go find a woman anywhere. They have to take whatever they can get.
The same with Christian communities. They can only marry other Christians. Thus their are fewer of them. Thus they end up eventually being with a distant relative. The mass exterminations etc don't help.