system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are inner cities filled with so many lowlifes such as junkies, muggers, rapists, drug dealers, gangsters, etc.?
gpt
In the US, part of it is because we made a special effort to attract poor communities (primarily blacks) into our cities by way of rent-controlled housing.

The original intent of this was ostensibly to provide better economic opportunity to the poor because cities were (and still are) the primary centers of economic activity.

However, this had the negative effect of concentrating poor communities into the city while they still lacked the skills necessary for the jobs that generally were needed in cities (professionals and skilled laborers). 

Crime became a "solution" for some members of these poor communities, thus motivating the more affluent (generally white, at the time) residents of the cities to move to out of the city to the suburbs, since they could afford cars to commute into work anyways.

This effect is also known as "white flight".

The end result in many cities is that there are areas in many US cities almost completely dominated by poor minority communities with high crime and unemployment rates.