It’s good that you’re asking questions but mate maybe make a ‘nsfl ask lemmy’ or like ‘ask lemmy after hours’ sub for these kind of super controversial questions. Not a good look for lemmy.ml’s biggest (?) sub to have such a controversial question here

It’s a tradition, like washing your hands is required by some religions.

I searched up

where?

You don’t have to look very far in time to see how inbreeding caused a plethora of issues to the Habsburg’s lineage in roughly 16 generations. Incest would make pre-existing genetic issues likely even worse, considering how close genetically the parents would be compared to inbreeding.