Ah, true. So trying to do good won't help him do evil, either. What if he tries to do something morally ambiguous, like stealing bread to feed a starving family?
If he tries to switch the track so the trolley only runs over 1 person, it will probably (harmlessly) derail and save everyone, but doing nothing is more interesting to figure out. He's a villain, and I would consider seeing people about to die and doing nothing while cackling inwardly a villainous act even though the "act" is actually doing nothing. Would malicious intent through inaction count for the curse? Maybe not.