There's a difference between "not paying taxes" (a crime) and "not paying a fair share of taxes" (legal, and essentially encouraged). I can't speak for Senator Sanders, but I don't believe the wealthy are illegally evading taxes; I just think there are a lot of aspects of personal and corporate wealth (and I'm speaking beyond mere income here) that should be taxed much more in order to provide more robust social services and a stronger, higher "safety-net" for all citizens.