Why are first cousin marriages allowed in some places

[oops_ur_dead]

I think there’s a second reason to ban it. The first reason as you mentioned: likelihood of genetic defects. Well we don’t ban people with genetic defects in general from having children so that logic doesn’t fit.

I actually think the laws come from older times where inheritance, noble families, royal families etc were more important. As a noble it makes sense to ban the royal family from incestual marriage because it forces them to marry one of you. Same with peasants and nobles. So I don’t have evidence but that’s my suspicion, because I can’t imagine why lawmakers would sit down and be like “incest is gross let’s ban it!” And not ban all other gross things or high risks for genetic defects, etc.

I don't think that's the case. Pretty much all of Europe which had those monarchies and feudalism haven't banned first cousin marriage. And of course, the US never had that stuff.