Warhammer 40k Imperial Guard Cadian
The source of magic in the setting is a parallel dimension of psychic energy known as "the Warp". All living creatures have a psychic link to this place, but certain individuals called "psykers" have an especially strong link and can manipulate its energy to work magic. Psykers are generally feared and mistrusted by humans, and with good reason. Firstly, psykers can possess many dangerous abilities such as mind control, clairvoyance, and pyrokinesis, and thus they need to be policed carefully. Secondly, the Warp is full of predatory creatures who occasionally use psykers as conduits by which to invade realspace. Because of this, psykers must be trained to control their abilities and resist Warp predators. Those who fail or reject this training are executed for the safety of all. Those who pass their training are pressed into life-long servitude to the state and are closely monitored for corruption and misconduct. However, psykers also perform critical services for humanity: their powers permit faster-than-light travel and communication, which are impossible under the "normal" laws of physics. A key theme of the setting is that for all the difficulties that psykers pose, human civilization cannot do without them.