I do not mean to sound condescending, but I don't think you really understand what goes on in large cities or other populated areas.
First of all, groups of men and women do police these bad neighborhoods. They are the police, and their job is not as easy as you seem to think. NYC is actually a rather safe city compared to most cities in this country. The areas or major cities that are the most dangerous are controlled by organized criminal drug gangs, who are totally ruthless. You are not going to have ordinary citizens going in there and cleaning the places up by kicking ass like a Hollywood movie. People who would try to do that would be killed. The only real way to clean these places up is to use good police work like they usually do in the safest big cities, and to get more business and infrastructure in these neighborhoods. Major cities have always been dangerous, and they will probably never be totally safe because violent crime will always go up when you put large numbers of people in realtively small areas.
Your point about the real mean is actually very true because many of the children in these areas have no fathers to raise them, so they grow up to be criminals because criminals recruit them and it is the easiest way for them to support themselves. I do not mean this statement to sound like an excuse for their behavior, but it is a big part of the problem.