Outlaw motorcycle gangs, organized crime, drug cartels and ethnic gangs come together for a common purpose that may start as a social thing but can evolve into something anti-social or criminal when the members who make up the gang are antisocial or criminals themselves.
Sociologists believe that a gang will take on the morals, or lack of morals, of the worst members and often exceed that lack of morals. This behavior often manifests itself in most or all of the gang's members, especially when they are together. This behavior can be explained as 'group dynamics,' which is essentially the way individuals behave when they are part of a group.
The behavior can become extreme. Such behavior is often displayed around the world during rioting. The riots that occur during or after sporting events or protests can lead individuals who may not be inclined to act in a violent manner to act in such a manner and exceed their own planned actions or expectations.
In the case of college students who usually display disciplined behavior and conformity, attendance at a post celebratory rally for their college's team can cause them to get 'caught up' in the more severe behavior of their fellow rally-goers. This can result in the usually behaved student becoming violent, undisciplined and uncontrollable.
This group dynamic that leads to bad behavior is also evident in so many of the "Girls Gone Wild" videos advertised on television networks after midnight. Individual behavior becomes elevated to the worse behavior being displayed by friends, as the crowds cheer them on with the presence of the camera and the brief opportunity for fame.
Many of these individuals, college students, girls going wild or gang members may later be shocked by their own behavior.
Several gang members have told me that they were dabbling in minor crimes such as graffiti and petty larceny before their membership in the gang but committed more serious and more violent crimes far beyond their nature and expectations as a member of the gang.