I think the very mentality that social inequality and "oppression" is the reason for gang activity (almost using it as an excuse) is a huge part of the problem.
Yes. There will always be social inequality. Oppression, however, is a victim mentality, and as long as this mentality is enabled in our society, yes, we will always struggle with finding solutions to every kind of crime.
My thought is rather than fighting social inequality, or throwing money and effort at groups of people who are unwilling to help themselves, we should providing opportunities for kids to overcome their backgrounds and rid themselves of the victim mentality.
There are plenty of successful people who rose against unbeatable odds and chose better lives for themselves, despite their background and family situations. Perhaps we need to be capitalizing on what these people site as the methods for their success.