That's exactly where the legal definitions of "offensive weapon" and "lawful authority or reasonable excuse" come in. If a person takes issue with these laws and the definitions therein, there are avenues for changing them or at the very least making their opinions known. Flouting them, either in protest or out of a sense of injustice, probably isn't the best way.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'