If you modify the thought experiment slightly, it becomes an interesting trolley problem.
Let’s assume the spell you’re using is all or nothing - either it cures everyone, or no one. What if some subset of people explicitly do not consent? How many people would it have to be, or what percentage, before you would consider not doing it? Obviously if only 1 person doesn’t want it, who cares, greater good, but what if it was 99% of people? Where’s the line?