what do you think was meant by the following comment on the six yard safety net that roger allowed while throwing stones in henry's direction: roger arm was conditioned by a civilization that knew nothing of him and was in ruins

Roger walks a fine line between the old and new world. He has this urge to hurt things and watch them suffer. We see this in his interactions with the "Littluns". Roger throws rocks at little Henry. Roger aims to miss because the rules from the old world subconsciously stay his arm. Somewhere in his brain lies the memories of adults and reprimand. These memories, however, are fading fast leading Roger to be the true masochist that he is.