Groups are what make up our lives. They are what define our values and how we fit in to the society that we are in. Even if we don't think we are a part of a group within a society, some way we always are. In the movie, Collogero becomes very close with Sunny, together they are a part of a society of fear. Every one is afraid of Sunny, so whoever is associated with him they will also fear.
Just like how they fear Collogero as he is growing up.
Sunny and Collogero are grouped together in a more specific place. They know that all the killings and bad things that Sunny does are bad, but for some reason they can't resist leaving it. They both know that it's better to just keep things the way they are. But as the movie goes on, Collogero changes and he starts forming his own groups and thinking his own way. As his dad always told him to stay away from Sunny, eventually Collogero realizes that everything Sunny does is hurtfully wrong. Especially when he almost went to attack the African Americans with his friends.
Even though groups are what can define ourselves and our status, eventually things can change. Collogero went from a little boy to Sunny's high top master status just from the group of fear.