Do gangs and gangbangers serve a good purpose in society? Has anything good ever come out from it?

Every single time I watch documentary about gangs and their lifestyle, it makes me angry how people can be so cruel and heartless to each other. And I often ask myself, what good does being in a gang bring? Whats the whole purpose if it seems that all they live for is to claim property, sell drugs, kill, and reproduce? I thought we as humans were more mentally advanced than animals, but it seems, that’s how most of them act….like animals…Why do they encourage hate and only make their lives worse instead of finding ways to love one another and to fix their problems? I’m not saying this to put them down, I’m just confused as to why they do this?...It breaks my heart to see how it affects not only their lives, but the lives that revolve around them, and the lives they ruin as a result of their behavior….why?