I don't think honorable conduct has much to do with success.
Many approaches work. Ireland, Israel, India, etc. all succeeded. I think one can do things in a very dirty way, and sometimes in a very clean way. It depends on the opponents and what they're doing, and the attitudes of the other relevant entities.
US manuals usually discuss this kind of thing as an early stage of destabilization, before things go to open warfare, and I think that's correct. I wouldn't say that it for sure is an effective way to creating something suitable for the kind of disorder where a revolution is possible, but I don't think that was Mangione's goal either.
I think this was personal-- that felt he that the company had wronged him or a group of which he was part in a way that he could not get righted by the courts, so that he had to obtain revenge on his own, but maybe I'm imagining him as having my own moral view of courts and the legal system-- basically, if they will not hear a matter where someone is exploiting me, they make themselves irrelevant and I can do what I like (i.e. imagine that you get shot, and the courts will prosecute people who shoot people, so you go them-- no need for personal vengeance, but if it was done by a diplomat, you beat him to death right there, because the courts wouldn't hear you-- i.e. by being willing to hear cases, take into account any kind of thing which affects you, the courts substitute for private vengeance, and I see this is their basic function, on which they've then built).