I disagree that Armstrong didn't approach that situation in good faith. I think he meant every word he said. Armstrong was a caricature of American Individualism and a diehard fanatic. If you watch his speech now, there's a lot in there that sounds familiar to modern politics. Including "they'll make America great again!"

He's a villain who comes off as a "might makes right" true believer. It doesn't matter if it's physical strength, underhanded tactics, cleverness, or sheer endurance. So long as you win, you make the rules.

He believed that the strong should squash the weak, while Raiden believed that the strong should protect the weak, and they both used violence to enforce their beliefs. In his eyes, neither of them were right. Who would decide the rules merely came down to which of them was stronger.

Raiden is Armstrong's beliefs made manifest. From surviving as a child soldier up to the very moment that he kills Armstrong, he's enforcing his will on the world around him through his strength. A shift in perspective, which side of the sword you're on, and Raiden's justice becomes the same as Armstrong's oppression.

This is the danger of a true believer of "might makes right." Because even when you beat them, you didn't prove them wrong - you merely played by their rules and beat them at their own game. Your might made you right, and nothing more.