@WandererUber @Terry @FourOh-LLC @Witch_Hunter_Siegfired @givenup @grey @veff @vic @TatsuyaIshida >Maybe the church was simply doing power politics against the nobles?

That seems much more likely than anything else, and it was probably only enforced on them if anyone ever. The blood relation at anything beyond third cousin is as low as 0%, so the idea that it's about genetic malformations or any other tropes is nonsense.