Over a long period of time, the notion of looking out for each other, helping each other, has been undermined precisely by the rise of the interfering state. That is the only reason these so-called 'vigilantes' look weird.
Teenagers carry knives because it makes them feel safer. They feel they need a strong means of protecting themselves from their peers who carry knives. We need to break this vicious circle - to persuade teenagers that there is a greater risk in carrying a knife than not.