I don't agree that it is always stupidity to allow that situation to develop.
For the majority of people, it's stupid. But is it for these people?
In the town where I work, there were 283 cases of crime recorded in June of which 252 were committed in 3 streets. It was generally drug offences, and anti-social behaviour.
This is a big town we're talking about, not a little village. If you were to grow up in those three streets, you would be living in a different society. One where crime was normal, where the people you are brought up to trust probably have criminal records.
Therefore the point isn't that this underclass commit more murders than the upper class(although I imagine they do) but it's more how the murders that do occur come about. The most sickening thing about this case was the level of trust that was afforded to this man to essentially look after this young girl.
Like it or not, over the last twenty years or so, there has developed a very worrying new social class that fit into the 4th tier.