@BowsacNoodle @Terry @FourOh-LLC @Witch_Hunter_Siegfired @givenup @grey @veff @vic @TatsuyaIshida Found some npr article about this, gives the source as a fella went by the name of "Joseph Henrich" evo bio at harvard.
they say by the end it was 6th cousin that was prohibited. That seems like nonsense because that's basically everybody you'll ever meet in those days.
The article felt like a retcon of jews jamming our ingroup-outgroup distinction into "the church broke up the clans and made everyone trust strangers". Even though hospitality to the stranger is detailed in the pagan Edda and is proven to be very old PIE practice.
Maybe the church was simply doing power politics against the nobles?

I'll do some more reading.