NO
To stop the threat.
A living perp is a perpetual threat. He's likely to show up in your back yard 5-10 years later after his release from prison.
NO
To stop the threat.
Exactly. Killing the bad guy may be a consequence of stopping the threat, but it should never be the main objective. The very first words you say to an officer (or 911 dispatcher) after something like this are the most important words you may ever speak. LEO's are there to collect evidence and document what happened. Saying "I was shooting to kill the guy" will not help you at trial.
“The lesson?... and shoot to kill.”
NO
To stop the threat.
Two words: Center Mass
Colonel, USAFR