Okay, you just killed a cop. What do you think happens next? Do you think its over and done with, just go home for the day? No, you are, at best, going to be arrested and put on trial for murder. It doesn’t matter if you were justified or not. And when they arrest you, it will be at gun point. So, will you let them arrest you at gun point or will you start shooting the police again?
You’re also assuming your some badass who will walk away without getting shot also or in any way injured. Not to mention the emotional toll of killing someone has on most people.