So you are faulting me for saying I have the ability to pull a trigger when I'm confronted with a criminal capable of mass murder?
Do you? Or do you think you do? ..

Do you also criticize police officers and security guards who are faced with such a decision and also pull the trigger?
Thats their job, see the difference? Them doing it cause thats what they are supose to do you, you doing it cause you think you hold the right to act the justices. But this been pointed out already, i dont think civilians should take such matters into their own hands, thats why the police exist.

Would you look down on the single mother who shoots an intruder trying to kick in her door and wielding a knife?
Thats a different scenario you know it as well, ofc you if you find yourself in a situation where you need to use lethal force to save your our others life its not optimal but necessary. This scenario of yours you would look up the bomber and then proceed to shoot him, if had attacked you it might been a different thing but since that havent been the case a call tot he police would be the best course of action in your scenario.

You look down on all those who defend themselves, or is it just me because I stated it in a manner not to your liking?
Not once in your post have you mentioned that he would play attacking part if you dont consider just hiding somewhere to be actively engaging in hostile activites. As you mentioned in one of your previously posts "If I found the guy hiding...."