That's stupid. You're stupid. Stop being stupid, stupid.
On an equally stupid theory, I'm pitching the assumption that Eibon is Shinigami's wife. Even though they seem to have rooted that Eibon is probably male.>>11918702
I think the general idea that calls for Witches to be hunted is that they are treading in occult practices that no person should be allowed.
No man/women should be able to freely wield powers beyond that of mortals kinda thing, even moreso when their acts would often result in harming others or tipping the favour.
I say 'freely' as the Shibusen are students being trained and taught to avoid abusing their abilities.
Though this is just my guess, could be wrong.