In theodicy, freewill theists lean on the notion that God merely permits evil to happen. The intuition is that if an agent directly causes or determines an event, then that makes him morally complicit in a way that just allowing, or not preventing, an event caused by another agent does not. A cliché comparison is the distinction between killing a patient and letting him die, in medical ethics.
And sometimes that’s a morally salient distinction. But sometimes not. Suppose I’m a guard at a Nazi concentration camp. Suppose I secretly despise Hitler and the Third Reich. I’m not there because I signed up. I was conscripted. I’m there against my will. I privately hope the Allies will win.
Suppose the commandant has a plan. If it becomes unmistakable that German lost the war, and the Allies are marching into Germany, the prisoners, including Jews, as well as Allied war captives, will be executed so that the Allies can’t liberate the camp. After executing all the prisoners, the Nazi personnel will evacuate the camp. Even though the Nazis lost, they will kill as many Jews and Allied war captives as they can on the way out. A final act of spiteful revenge.
Suppose I have a choice: I can stand by and let the prisoners be mowed down, or I can turn my machine gun on my nominal comrades and save the prisoners. Under that scenario, is inaction morally preferable to action? If I do nothing to prevent the massacre, does that let me off the hook? Conversely, if I take direct action by shooting the commandant and his henchmen to prevent them from murdering the prisoners, am I culpable?