It's all about The Prisoner's Dilemma. The rich and the powerful have too many of us convinced that, if we join a union, we will never be either rich or powerful ourselves.
Fact is, most of us will never be rich or powerful no matter what. By joining together, we can be better off than we are, by quite a bit. But that's a hard sell in a world where it is possible for a grifter to become the president, and a jack-ass to become the world's richest man.
