The ethics of raising a zombie army

[Psyren]

True. And with the Cavalry of the Dead trope, the dead still possess free will, and come to the aid of the living out of a sense of duty.

Well, coercion might still play a role - Aragorn's dead were obligated to answer him because they failed the previous king, and were cursed accordingly - but that ultimately stems from an authority they were beholden to in life, not some random unrelated spellcaster showing up later.