Justify the theme of Lawlessness

On the one hand, Doyle is clear about morality within the story. The Scowrers are practically irredeemable, characterized by near-senseless violence. They tolerate no threat to their authority and menace innocent people. However, McMurdo poses a more interesting moral conundrum for readers. While he is undercover with the Scowrers, he beats, threatens, lies, and most likely kills people. He also watches and says nothing in many of these situations, though he does warn Wilcox and saves Stanger from being beaten to death. One wonders if he is just as bad as the Scowrers even though he eventually puts them away. It is perhaps easier to say that he is doing a good thing, but without knowing just how fully he participated in their bloody deeds, it is impossible to say so definitively.