Would you defend your defenseless neighbor, before or after, the intruder came into your home?
Before if I knew he would attack, obviously. Though I would not just shoot a man on the street who had done nothing. If I had reason to believe he would attack my neighbor I would call the police and warn my neighbor.
I've told a couple of libs that since they don't like guns and think they're 'bad', I would never raise my weapon in their defense (since I didn't want to 'offend' them) and then they get all snippy!!!