Preemption

All my dreams came true last night
All my hopes and fears
All my dreams came true last night
In tears, in tears
--ABC

A sinister looking person is walking toward you. You fear for your life. Is it within your right to self-defense to act on that person to eliminate the perceived threat?

No.

A person who has indicated dislike for you buys a gun and trains with it. Is it within your right to self-defense to hire strong-armed agents to take the gun away from the person?

No.

A person who has indicated dislike for you is walking down the street toward you with a holstered gun. Is it within your right to self-defense to act to disarm that person?

No.

Preemption is rarely a legitimate reason for applying force against another person. Only when a threat is acutely imminent (e.g., a person within a few feet of you draws a gun and says he is going to kill you) is preemptive action potentially valid.

Otherwise, preemption is aggression.