My most charitable take is that Dumelo didn't understand the damage he could do with the blade. He's always appeared really dumb, but still smart enough to be aware of consequences. Like when he stabbed Austin, he took steps back and hesitated like he thought "no fuckin way." Then he ran, then he didn't totally flee, then the dumb stuff he said to the cops, then his crying in the courtroom. I don't think he's actually as evil as people make him out to be - he seems genuinely remorseful (unlike his family and the nigger hoard around him).
But it's just another tragic example of why niggers need removed from human society. *At best*, they're too dumb to understand the consequences of their actions, as they're too dumb to understand much of civilized society and technology. At worst, they're maliciously-violent psychopathic predators. They are the pitbull of humans... dumb, savage, and unpredictable to the point that you can't even really call them dogs/humans.
In the charitable mood I'm in, I'll follow up by saying just about any nigger I've encountered who's ever enlisted seems to be okay. Which makes slavery make more sense in context - if integration is to be, it's only through heavy-handed discipline and moderation of nigger. But frankly, I think we'd be better off not wasting our time and just removing them all.