Really thought provoking message to this movie.
First, look at the poster. He looks like a primal warrior... A Viking. Man in his natural state.
How does he start off in the movie? A soft, suburban stockbroker, feminized by modern society's expectations. He goes to prison and ends up a powerful warrior. A primal, barbaric man. He doesn't even want to get out of that life once he's in it. He actualizes his true potential as a man in prison.
This movie is trying to say that true masculinity is so dangerous to modern society that the only place for it is in prison.