How To Break the Cycle
By themselves, these "squishy" liberal ideas won't stop the cycle of gang violence. What we have is the classic difference between breaking a cycle versus preventing the cycle from forming in the first place. It is fairly easy to prevent these cycles from forming; give every child a solid education, make sure jobs are available for all adults, practice community policing, etc. While gangs occasionally form in middle class neighborhoods they are easily dealt with before the problem gets out of hand, before the cycle of gang violence forms. We need to implement more "squishy" liberal ideas to prevent these problems from forming.
It also helps to have the economy grow in a nice, reasonable and boring rate. Economies that lurch to dramatic highs only to crash to violent lows just kill the poorer families. Each time the economy stalls a few more of the poorest among us fall out of the system. Steady economic growth supplemented by reasonable safety nets will do more to prevent the future formation of gang, not to mention the homeless.
But breaking a cycle that already exists is much harder than mere prevention and I don't see any clear and obvious solutions. My guess is something truly draconian is needed to break the cycle. But for me the take-home lesson is don't allow these cycles to form in the first place.