Those examples though, they seem more like righteous indignation than 'darkness' so to speak. Seems like the kyubi latched on to Naruto's anger at the death of a friend, or at the shit talk of a hated foe. What seems artificial, is something different from that. It's Naruto's persistant even if well tucked away, resentment towards the village. Ever since Iruka hugged Naruto in that first episode, there's been very little if anything at all to show that he was harboring such emotions. He's always come across as friendly, loving, and most importantly, genuine. To now try and say Naruto's actually been a little phony all this time is going to require more suspension of disbelief than should be necessary.

If mastering the demon is going to require mastery of anger, as a general emotion, I can accept that. It'd be nice to see Naruto as a zen master. But if it's 'darkness', as in the petty things, the secret things, the weaknesses that lead to evil, then it just seems to me like another breaking of an established fact in the Narutoverse. Naruto is genuine and good. TBH, that's always been kind of a bore, but to try and change that NOW requires far more than it looks like we're going to get.