I haven't heard anyone claiming that "gangs are good" or suppressing debate about the pros and cons of gang violence. In fact, I've heard and seen a lot of good

I haven't heard anyone claiming that "gangs are good" or suppressing debate about the pros and cons of gang violence. In fact, I've heard and seen a lot of good work by many parties concerned about the negative influence of gang activity in the US. However, such discussions are definitely a red herring when advanced in the context of police violence--an entirely different and largely unrelated problem. Heart disease is the leading cause of death among African Americans in the US and I hope someone's working on that, but if you argue that racially-skewed police killings aren't a problem because of heart disease then it's entirely expected and reasonable to be met with complete silence or active suppression.