There’s a distinction in law between malum prohibitum and malum in se, or rather, between what is considered unlawful and what is considered evil. In a Western, you don’t have to worry about the difference. A son-of-a-bitch has it coming, whether it’s malum or not to kill him. Western lawmen are vindictive. They serve out justice. They do not enforce statutes. When a man kills a little girl’s father; it doesn’t matter why he did it, or what socio-economic forces led his morals to corrode. That son-of-a-bitch is going to get his just desserts. Never mind the moral quandary of “an eye for an eye”. In True Grit, the hero only has one eye; the better to see malum in se, the better to look at the world through a gun-sight.