I think it is the predictable and in a sense understandable outcome - to an extent; opposed to it being the right one. For it to be RIGHT - it has to be morally acceptable; and with the question of morals, in MY opinion it is not the right thing to do. Please, this is my opinion - feel free to have your own.
Before I start; i would like to point out that I am not a Sasuke fanboy, or any fanboy for that matter - as I think all the characters have their roles - which has resulted in a great Manga and Anime series.
Anyway, if you actually consider the perspective Sasuke is coming from - to a young adolescent, when your clan dies (when you are young); ad knowing Sasuke has already trained his life for one objective, it is guaranteed that he would go for revenge; initially on Itachi. Up till being a Genin, he has slaved away trying to excel to the best of his ability. Eventually, when he finds that it is not enough - he no longer really sees reason, or what is morally correct. No, all for him - is that 1 objective... revenge on the person who killed his clan. Up till now, it was really quite predictable, if you noticed the mental strain on Sasuke; when Naruto steadily decreased the gap; up till guess what - Naruto's Rasengan proved to be capable of a bigger destructive effect that Sasuke's Chidori.
We all know what happens next - Sasuke's move into darkness etc etc
However, lets skip to the bit where he fights Itachi. Now initially he hates him with a visible intensity, but at the end of the battle - in a perfect scenario for Sasuke, he wins, goes back to Konoha or lives his life out of trouble - that is the positive outlook, could be worse for all we know.
However, it didnt happen like that. He was down for the count - he was dead almost as soon as he fired his Kirin, he had exhausted his Chakra, and Itachi - has his Susanoo. With help from Orochimaru he lasts till Itachi effectively exhausts his resources as well.
Now when Tobi tells him the truth what does Sasuke think? He realises this whole time, he had been aiming for a hero of Konoha, a good person. What can he do? Go back after all of this? To face what? Angry with himself, but even more - at those who caused this in the first place, like an angry teenager, Sasuke justifies his 'only option' - destroy Konoha. Convincing himself, really couldnt have been that difficult - with Tobi there; and his own limited options.
The rest, we are aware of.