The Dark Lord’s "prophecy', His vision, His dream that Draco was charged to achieve.  Of all the Dark Lord’s followers, Draco hated one above all. Powerful, yes, but unruly. Uncivilized. To lose oneself to a curse just once every full moon seemed a small price to pay for the power, and horror, the curse bestows. But to be a snarling brute all your days on the earth?