The bad side of this loyalty is that they can never really have friends outside the gang. They spend all their time with the gang, and must do whatever the gang leader tells them to do. They lose their freedom when they join a gang. In order to join a gang, you have to prove you are worthy by going through a process of initiation. In some gangs, initiation involves committing some kind of crime.
Initiations are generally very brutal.
Today the use of guns is quite common in gangs. Most gang shootings involve other gang members. But recently more and more innocent bystanders have been killed by gang shootings. A gang's main duty is usually to protect its turf. Simply wearing another gang's colors on a gang's turf is reason enough to be killed.