I disagree. Cities are fine and the people in cities are alright in different cultures. The problem is the culture, not the population density. I think it's a situation where strong cultures can sustain a high population density and be fine, while weak and atomized cultures degrade into mob rule.

The real problem is that USA culture, and all of Western culture, is mob rule by default. When you get these animals together in high enough concentrations they murder each other.