The five stages of grief are denial, anger, bargaining, depression, and acceptance.
He's stuck on anger because Konoha keeps fueling flames.
Following the massacre he could feel the denizens of Konoha all around him.
Konoha went out its way to make him feel not alone and in the end they made him worse.
They didn't understand that Sasuke was desperately afraid of getting close to anyone and their constant attempts to include him were driving him further and further into himself and deeper into vengeance's maw.
His classmates tried to close and his fan-girls were open about their desires on getting close to him and he wanted to scream and shout because he just wants to be alone.
Sadly his desires will be ignored because the children are children and the adults don't realize that he needs to be alone in order to come to completely remove the love he holds for his brother in his heart* in order for him seek justice instead of vengeance.
Indecently this is why he will respond^ to and eventually become Naruto's friend, Naruto left him alone.
Years later when he is forced to relieve to relive the massacre he desires to fight Naruto to remove their bond. He figures that if he can cut off that bond he should be able to remove his love for Itachi in his heart.
He heads to Orochimaru to gain power because the memories are too much and he wants to completely sever the bonds he has to both Naruto and Itachi.
When he finally kills Itachi he feels dead inside because he doesn't know what to do now and when Madara tells him tale about Itachi he instantly believes it because he was never able to squash out the love he holds for his brother in his heart.
When Danzo confirms the tale and makes it truth he is so enraged that Konoha used his older brother that he swears to completely crush and kill everyone one of them for their crimes against the Uchiha.
Konoha viewed the Uchiha clan with suspension following the Kyuubi because Madara could control the Kyuubi, forgetting that Uchiha turned their backs on Madara.
Konoha made the Uchiha relocate into a corner of the village and confirmed Madara's objects. In response to Konoha's actions the Uchiha planned to rebel to secure a better future for themselves.
Konoha used someone traumatized by war to end the threat they caused.
Despite this apart of him still cares for Naruto and that is why he has accepted to taking Itachi's eyes.
He wants to completely sever the bond between them.
It's as simple as that.
Nothing more, nothing less.
Author's Note: While I don't condone Sasuke's desire to kill every single person in Konoha, I do recognize that he is Konoha's victim.
Every hidden village does fucked up shit and none of them like having to actually admit that they fucked up and are not perfect. Konoha is no different.
*Considering on how Sasuke was quick to believe Madara it's reasonable to assume that a part of him always loved his brother.
^Sasuke could of just ignored Naruto like he did Sakura, so I figured they had to be a reason he responded to him in the beginning of the series.