Was the Necromancer for Real?

There are two schools of thought regarding King Shaul’s (Saul’s) use of the Necromancer to raise the spirit of Shmuel (Samuel) from the dead to inquire about his prospects against the Phillistine invasion force gathering at Beit She’an.  The rationalist school, followed by Rambam, Rashi, etc., holds that it was entirely an act of smoke and mirrors, and there is no reality to black magic or witchcraft.  The alternative school of thought, mostly Ramban and those with a more Kabbalistic bent, holds that dark forces are very much real, but Torah forbids using them.