It's obviously all down to interpretation on what a gang really is.
Lets see what the dictionary says:
1. A group of criminals or hoodlums who band together for mutual protection and profit.
2. A group of adolescents who band together, especially a group of delinquents.
3. Informal A group of people who associate regularly on a social basis:
The whole gang from the office went to a clambake.
4. A group of laborers organized together on one job or under one foreperson:
a railroad gang.
So obviously the first two definitions associate the word with criminality. And that's probably what most of us think of when we hear the word "gang". It's the most common use of the word so any other meaning (eventhough it validly exists) would sound odd. Like saying someone's gay? The first thing popping into your head wouldn't be that they're "happy", would it?
