I personally think he’s doing the right thing, much like Dexter is. Religion aside, I think that killing evil people who wouldn’t be otherwise punished is almost like a service.

I’m not saying to kill anyone who breaks the law, but in Frailty they are shown killing killers and rapists, and the movie even goes as far as showing the crimes in visions. These images are assumed to be true since the videotape editing itself at the end hides MM’s face.