As for Riddle, if it wasn't for the pointlessness of it, Harry would have done him in by now. But his own High Dark Death Eaters - cunts like the Lestranges and Dolohov - would have simply killed a random passer-by, used their body mass to reanimate their Dark King with his Last Horcrux, as many times as there were victims to be had. Harry didn't want their blood on his hands. Good, pure blood. He intended to shed so much blood of the evil kind that he doubted the train in the afterlife would accept his spiritual Oyster Card when the time came now.