I understand that Sasuke learns Itachi was motivated by his desire to protect the village. Itachi only slaughtered his clan because they were plotting a rebellion. And thus Sasuke's motivation for killing Itachi was slightly misguided. Since Tobi told him about Itachi, why does he want to destroy Konoha? Itachi died protecting it so why does Sasuke wants to destroy it?
He wants to destroy the village that put his beloved brother in the position to choose between his family and his village.
Sasuke can legitimately be thinking that if given a command to kill all of your relatives, the people who gave that command are evil and should be destroyed.
Don't forget that when it comes to family, very strong feelings can easily be affecting Sasuke.
Really, Itachi choosing the village over his family was the abnormal decision.
Both times, it was revenge.
Initially, he wanted to avenge his clan's murder from his brother Itachi and later, on knowing that the attack was ordered by the Leaf Village elders and, in order to protect Sasuke, Itachi had to kill the entire clan by his own hands, his revenge spirit was against the entire Leaf village as a whole.
In the manga, the Second Hokage has mentioned that the Uchihas love their family more than any other any ninja. In fact their Sharingan evolves when they fight for their loved ones and also have this tendency to go evil and on an irrational blood feud when their loved ones are harmed or killed. The same happened with Madara Uchiha when his brother was killed.
Its Revenge for his family and his Clan. & He call him self avenger for same.
He chose to leave village and become student of Orochimaru because he wanted to become stronger than his brother and then Kill him(Itachi). & In order to Kill Itachi he have to be powerful enough so he joined Orochimaru to gain power and learn new jutsu. So he can take revenge to Itachi.
When Tobi(Obito) tell him false tale of How leaf village commanded Itachi to murder whole Uchiha clan which turn Sasuke's feeling to avenge Whole Village for forcing his Brother to do this cruel act. & decided to destroy leaf village.
I think these two things make Sasuke Evil because first he was wanted to revenge his brother for sake of his Clan & Family in any cost. & then Secound when he come to know about Itachi's sacrifice of whole Clan & family for sake of Village.
From the first show Naruto in season 1, episode 29, the snake that bit sasuke in the neck made a mark of evil, soon he was gonna release or seal the snake power.
Sasuke wanted to get revenge on itachi and restore his clan and family,in order to gain new Justu, he had to leave the village and team 7.
sasuke undersand that danzo force itachi to kill his clan becase there is no one is stronger itachi so the use him say wepone and kill whole uchiha clan but he could kill his own brother and sasuke hate him before he dnot know turth but toib told him all turth he lies so that why he tries to destroy leaf but itachi told him and now try toprotect leaf