Well...think about it for a sec...would you 1)..conserve chakra and just take her kunai and kill her with it...or would you 2)...use chakra would probably don't have and would have to strain yourself to use....hurting himself more....And I noticed you said the whole him trying to kill sakura thing seemed sketchy also, I thought that to, he had her by the neck he could have easily used chidori and been done with it I think maybe somehow he knew zetsu was there im kind of on the fence about this theory the cause everyone is insisting that he was for sure trying to kill her. I think you are probably one of the only people who agrees with me on this lol