They have power over the millions of souls who are asleep. In order to easily conjure and defeat a black magician, you need a lot of awakened consciousness and a lot of energy.

We do not need to be afraid of black magicians. They can only harm us by taking advantage of our stupidities. What we should be concerned about is how stupid we are, and how easily we fall victim to our pride, laziness, lust, etc.

Whatever harm an enemy may do to an enemy, or a hater to a hater, an ill-directed mind inflicts on oneself a greater harm. - Buddha Shakyamuni, The Dhammapada