Although Daniel Penny was not armed with a gun, he was armed with the right mindset: he knew that a determined person can take down an attacker, even an armed attacker.
He is actually a very modest, introvert guy who never sought any kind of exposure.
What a communist prosecutor, an incredibly evil woman, and a corrupt judge tried to do to him is an outrage - and they almost succeeded, despite all the evidence and witnesses in Penny's favor!