It's also possible that ARod truly believed he would get "fair" treatment. Braun made a mockery of the appeal system, publicly destroyed the handler's reputation, attacked his accusers in the media, etc. And he got a nice tidy offer of 65 games and a fresh start this season.
MLB clearly wanted to make an example of ARod and went to extraordinary (unethical/illegal?) measures to bring him down. I'm sure that factored into ARod's defiance. He may have started to see himself as a victim - and in some small way, if you're comparing him to the treatment and suspensions of others, he was.
MLB got the result they wanted, but I think they hurt their own public credibility a lot in this as well.