" The same thing is happening to Draco under Voldemort’s tyranny. He is being forced to cast the Cruciatus Curse against fellow Death Eaters under threat of punishment if he disobeys. Harry sees Draco’s “gaunt, petrified face” and feels “sickened by what he had seen, by the use to which Draco was now being put by Voldemort,” understanding that Draco is obeying against his will in order to protect himself and the rest of his family. "

― Lorrie Kim , Snape: A Definitive Reading