as hard as it is to accept, a lot of the issues were imported by immigration and a failure to make sure that the immigrants get integrated into society. from what i know, there's a pretty deep divide there, with immigrants being disadvantaged in society and the swedes themselves feeling overwhelmed by a flood of immigrants. Sadly that's a good substrate for gang violence and yeah, like you said, it's stupid.

Edit since people seem to misunderstand: The failure lies in the integration, not with the immigrants. Sweden imported a lot of traumatized people and neither gave them therapy nor the means to function in swedish society a.k.a. education so they can get jobs. The gangbangers today are second or third generation immigrants mixed with the lower class native kids, all of them inherited the trauma from their parents through abuse and addiction. All of them share that they don't have a perspective for the future that would give them a way out.