If you had the opportunity to kill an evil person, i.e. Hitler, Dahmer, would you?

Yes. If this opportunity comes after the act of evil, and may prevent further a recurrence. 

Yes. If this opportunity comes after the act of evil, even if a recurrence isn't likely. 

Yes. If the opportunity comes before any act of evil, but there is substantial reason for many to believe an event is near. 

Yes. If the opportunity comes before any act of evil, but you alone know an event is near. 

Yes. If the opportunity comes before any act of evil, but you believe an event is near. 

Yes. If I could get away with it. 

No. It's not my responsibility. 

No. It goes against my conscience.