In the real world if somebody says “I’m going to kill you” they have given you a green light to respond with extreme prejudice.
I couldn't agree with you more. What are the US/Israel waiting for?
In the real world, if somebody has made clear his desire to kill you, AND has the imminent ability to carry out that stated intention, then you have the self-defense right to terminate his ability to harm you. If he desires to kill you, but has no ability, or has ability but no desire to use it, then you are not in danger.
For decades, the USSR had the ability to destroy us, but this did not trigger an attack by us, because we could be sure they did not have the intention to enter into "mutually assured destruction". But when a country whose religious philosophy GLORIFIES dying while attacking an enemy, then mere acquisition of capability becomes a justifiable reason for terminating their ability to strike.
Former FReeper Richard Fernandez (Wretchard), lays out the scenario in his Three Conjectures article.