If Sasuke was a straight antagonist, that's probably the route Kishi would've taken. But Sasuke's entire mindset towards what he's doing changes thanks to meeting with Itachi & the Hokage's. He isn't like Aoshi who needs to prove something against the protagonist, Sasuke's looking past everything going on and thinking of the aftermath.
Sasuke goes from being very self-indulgent, getting that good-feeling anger going. He knows what he's doing is justice (for him), he genuinely believes everything he says and that Konoha deserves what it's getting.
But after talking to the Hokage, Sasuke now feels responsible to keep the world safe, if only for Itachi's sacrifice. He can't be that same crazy energetic villain, because his purpose isn't coming from that manic self-righteous anger. He's now on a mission for someone else's sake.