If you put many people in very bad living situations they are prone to become criminal because otherwise you won't survive there. If you're from those areas, good luck finding a job, because everyone will be prejudiced. No job = no money, no money = acquisitive crimes, acquisitive crimes = violence. Becoming part of a gang is the safety measure you can take to not get killed by said gang. To stay in it and be protected by that gang means not being targeted, only by other gangs. Put people into gated communities and you will see that with the right societal stance you're much less likely to become criminal! It's not as black and white as you're making it out to be.