I want all the brutality to stop, not just the murders. Any effort to prosecute will get so watered down that only the worst will be punished so we can act like we're doing something about the problem.
Structural issues which create gangs need to be addressed, and it's true that convicting the gang members might detract from the need for those structural reform, but enforcing laws is still a part of the incentive system we have to encourage people to not break the law.
We should fix structural issues, but that doesn't mean we need to leave clear bugs in tact to increase pressure on fixing those issues.