This is where it get messy, I'm in house and did not threatening anybody therefore leave straight away, so how many people would shoot me in the back in the heat of the moment because you're angry?
You are clutching at straws with your argument.
The scenario you are playing out can happen without or without guns. People have defended themselves and killed intruders without firearms. People have also took the law into their own hands and dealt out further punishment after the intruders have fled, again without guns.
Having intruders in your house is a highly charged and emotive occurrence. Bad things will happen with or without guns. The only difference being is that with a gun the homeowner wrests some of the advantage back.