Most people would defend the lives of themselves/family if push came to shove - the law allows for that too in terms of 'reasonable force' . If an assailant has a lethal weapon, using a brick would be perfectable reasonable
If someone had killed/was trying to kill myself or my family I would respond as best I could,in self defense and anger probably but that doesn't mean I could kill them,not sure I would have the strength,if I say had to beat them with a break,especially if they had a gun or a knife I probably wouldnt survive.
I think everyone has that survival urge and if its triggered would kill in order to survive, protect etc. i can honestly say if it was a choice between me and this person attacking me i would kill them.