Perhaps your "gist" was to just dial 911 and wait for the infantry to arrive. The problem is that when some of these folks feel "wronged", they can go to great lengths to get even. Including throwing things through your windows or setting fire to your house. I suspect it's likely he accused the older man of "stealing" his crack pipe and made threats about getting it back, but that is only supposition.
It almost sounds as if you're advocating shooting someone for what they might do in the future.
The simple fact is that the shooter was safe in his home. Whether it took the police 3 minutes or 3 hours to arrive, he was not in any danger until he decided to leave the safety of his home and confront someone much younger who was likely high on crack.
Now someone is dead. The shooter may be charged with a crime. The BG may have friends who want to get even and the police probably have the shooter's gun. The homeowner may be suffering psychologically from having taken a life. For the life of me, I'm still not seeing any benefit for the shooter.