I think we all tend to join or make groups. Mostly we view them as benign and for many of us membership is as open as buying a house in the neighborhood, joining a club or graduating from a school or University. For all of us the membership is selective though, limited to a certain number by verity of skill sets, finances, language or any of numerous variables. In fact based on the skill one chooses one will find one is a member of many different kinds of mafia.
The real thing about the mafia is not that they go around hurting or intimidating, it is that not everyone can join. It is an important part of our view of ourselves that we can be selective and indeed that we can be selected. And we may excuse those mafia we belong to because we gained membership by legal and utterly benign means, whether by passing an exam, joining a career path or marrying someone. But the fact that we use and delight to some extent in all these things should not blind us to the fact that we cannot all be members of the same club or set. And that some clubs and sets are seen as being higher attainments than others.
I might not wish to have, I might not planned to have, but I have crowded others out by simply doing what I do.