Not at all.
According to Lt. Col. Dave Grossman, a military psychiatrist, in his recent book "On Killing," only about fifteen percent of troops on active battlefields will actually shoot AT the enemy. And these are troops that have gone through the military indoctrination designed to break down the very natural aversion most people have for taking another human's life.
I recommend the book to any and all Interested in the subject.
I haven’t read the book, but hubby told me it is way different if the enemy is directly a threat to you or those close to you. I would think it would be far different to shoot at someone you are told is an enemy than someone that is a direct and imminent threat to you or even someone close to you.
I would think self-preservation/strong will to live would kick in for many if it came down to it- especially if they prepared for such a possibility ahead of time.
With all due respect to Dr. Grossman, this doesn’t really apply in the case(s) that can be envisioned in the question on this post. The anonymity of a mass of men is not the same as facing somebody robbing your home or your store, or (in a post-EOTWAWKI situation) defending your family from marauders trying to take your food away. Abundant evidence shows that even regular people will be willing to take somebody else’s life in such cases.