Well, first off, vigilantism is actually illegal in most places around the world and you are not allowed to run around in a domino mask beating up criminals. Real-life costumed heroes (yes, there are such things) get around this because they just tie people up and call the police. The Green Hornet has been more, shall we say, proactive in his crimefighting. Shooting people with a poison gas gun (even if it only knocks people out, that still counts as poison!) and beating them into unconsciousness definitely crosses a line.
However, more relevant and important is that the Green Hornet makes a real effort to convince others that he is a criminal, and that he only fights crime to get rid of competition. He spreads similar claims as Britt Reid through the Daily Sentinel. He also takes a lot of the blame for the actions of other criminals, and never corrects people on which crimes he isn't guilty of.
