At the press conference following the Cannes premiere of Martin Scorsese’s Killers of the Flower Moon, someone asked Robert De Niro about his character, a kingpin of a sort with a tricky psyche. “It’s the banality of evil,” he said, describing the character’s moral ambiguity. “It’s the thing we have to watch out for. We see it today, of course. We all know who I’m going to talk about, but I’m not going to say his name.” (Everyone knew who he meant.) The banality of evil was hot at Cannes this year. De Niro’s statement came on the heels of...