Chye Isuel:
they parade them around to the public, and make them bear signs stating their crimes. punishments include not only an execution, but undead servitude is part of sentencing. the haderum is grim, indeed.
That grimness comes from their religious philosophy concerning the soul and it's state after death: The body and soul have a continual link after death, as the body suffers
so does the soul (or at any rate they preach this and many believe it so it makes a really good stick to beat the masses with).
To this end it is
HIGHLY ILLEGAL to create undead or muck about calling up dead souls for chats, regardless of whether or not certain Guilds or Nobles get up to these very sort of shenanigans (said Guilds probably have a charter allowing them certain flexibility, but your standard Joe McStreetdude does not).
However, as with most things, what the rich, powerful, or incharge get up to is often quite different than what we, the lowlies, can get away with.
I'm quite sure that any open Necromancers are highly regulated and licensed and don't ever do anything even remotely untoward. Ever. Not even a bit.
At least that's how I see it. My take could be wrong.