Necromancy is one of the most taboo forms of magic in Thedas, nearly akin to the reputation of blood magic because of its association with the dead - this is true even in the recent Dragon Age: The Veilguard. While it isn't outright outlawed in most of Thedas, it's so socially taboo that most mages avoid it, and most Circles don't teach the practice. Despite this, Dragon Age: Inquisition offers the specialization to the Inquisitor by bringing a necromancer to teach the Inquisitor and Dorian, one of the Inquisitor's companions, specializes in the school.