I really don't see how anyone could vote no on this. The premise here is that you either kill someone, or they kill you or someone close to you. If you don't kill them then either you or someone innocent dies. What purpose does that serve? Instead some psychotic bastard will live at the cost of someone innocents life. I suppose you could try to injure them instead, but that isn't necessarily an option. You may not be able to simply injure them without killing them. Sometimes its the only way.
Psychotic bastard posing immediate threat to you or those you might care to defend is a narrow and specific set of circumstances.
Psychology would tell us there is a serious aversion to killing things in most people, the first place most would meet it is in the discussion of weapons and range -- club is further than teeth and nails but still requires effort and gets you blood splattered, so we have spears, so we have bows, so we have firearms (ish and then definitely), so we have artillery... Also good is the rationalisations that some non combat military people use -- you might be a chef, a navigator, a bomb loader, one that loads the shells in a ship cannon and you did not "do anything to hurt anybody", but back in the civilian world I build a bomb and am nowhere around or pressing buttons to arm it and I would still get the book thrown at me, or I knowingly drive the truck to the parking lot and put it under that nice support section and same again.
There is also the "contagious gunfire" issue to consider -- if inexperienced people are pointing weapons at each other (though experience is hardly a sure fire dodge for it) and someone fires, or even sometimes a loud noise is happening) then it all kicks off and people potentially get hurt. It is why the adrenaline and guts comment a few pages back got the response it did from me.
Similarly others already mentioned the various degrees -- I already mentioned I think stand your ground and castle doctrine are dangerous and silly laws.
Equally I have some people I would consider truly pacifistic.
It is also not necessarily some psychotic bastard -- desperate people exist, otherwise mentally ill people exist, people that have not got a clue exist (see also make things idiot proof and you only create a better class of idiot), people that also do not have a clue about how dangerous things are (kicking people in the head is bad news, glass will ruin someone's life easily enough, knives are known to most people by virtue of them eating dinner most days and tend not to run out of ammo), drugs can make some interesting things happen though I might put that under desperate people.