Bullies and thugs do not always back down, especially 17 year olds with something to prove. Telling a thug who you know has already broken into your house once that he missed the gun is plain stupid, unless you're never going to leave your home.
I've seen things like this escalate to violence a number of times when I was on the job. Our instructions were to always try to talk people down from that ledge. Things get out of control way too quickly in one on one situations. This thug is backed by a gang? A bunch of anti-social punks who think an insult or a challenge to one of their crew is a declaration of war? Yeah, advise the civilian to beat his chest...that'll do it.
Did you read the original post? It's this persons step child and it is not their house that the thug broke into so the thug knowing that the other biological parent and step parent are ready to take action if they have to would certainly be a deterrent.
The cops don't do their jobs anymore so maybe the "civilians" need to start taking care of things on their own.