I've never had to shoot or kill anyone, I'm glad to say. But, anyone who carries CCW or is LE should have done some mental preparation for that possible event.
I have a very good friend who is about to retire from LE, after 30+
years with LA County SO. He's a homicide detective for over 15 years, so he's familiar with all sides of death. When he was in patrol 20 years ago, he rolled to an armed robbery at a Stop 'n Rob, and as he pulled up the BG was running out the door and started dumping rounds at him. My pal shot better, and dropped him with his Python.
He's not a touchy feely guy by any means, nor is he a super macho. Just a thoughtful, conservative cop, good family man, good friend. He said to me once, about the shooting: "You know, I think about it a few times a week. I don't feel bad about killing him...in fact, I had no choice and he was trying to kill me. But I think about it all the time."
It seems to me that's how I'd feel (I hope). I'd think about it, know I'd done the right thing, had no choice, but wouldn't brag about it, I hope. Better him than me.
In reading some of Col. Dave Grossman's writing on killing (
http://www.killology.com/ ) the military has spent a lot of effort to counteract the natural human aversion to killing, in order to train better soldiers. IIRC, the # of shots fired vs. enemy casualties in WWII was a high ratio compared to VietNam and now, as we've figured out how to train people to kill more readily. Interesting topic.