If someone killed one of my children in the way that this man killed, I would kill him for retribution.
A justice system protects him from my wrath. And protects me from the wrath of his father once he learns his son is dead.
Judicial system is amazing. What we need to do is to make it more precise by reducing false negatives and false positives.
Just because of a few failures of the justice system (the stories of failures you read in the news) does not justify getting rid of the entire system.
Revenge killing is good movie plot, but not really the reality of western culture nor was for it reality in past.
Moreover, other phenomenon in low legal justice areas is that if you or your family is not powerful enough, you suck it up and shut up when someone more powerful kill your relative. Or even when equal does that, unless you are connected to one of mafias. The average person when they have relative killed in drunken auto accident wont kill in revenge.
Even criminal groups more often kill for profit or to get rid or witness then pure vengeance.