That art style, ugh! It's as if the animators (and the manga-ka) had never seen a dog before, much less seen one in action. Not to mention their mouths are open ALL. THE. TIME.
Weed is averse to actually killing, but will still leave some that he fights to a fate worse than death? Kamakiri had his fangs and testicles ripped off, and it was implied that after Weed and his group left him, he was eaten by crows. Ouch.
It could be that people wanted to keep Weed's hands clean, so to speak, so he'd still be innocent. It seems to have backfired a tad though, at least where scenes like that are concerned. Leaving a badly wounded enemy to die in such a condition is pretty harsh for anyone.