Sasuke in the current time line, is nearly deranged, so obsessed with his goal of revenge that he's completely lost sight of all his morals. According to another character in the series there is a 'dark' power in him now, nothing like what he once was. Whether Sasuke created this darkness himself, or whether the seeds were planted by another is yet to be seen. What matters, is that Sasuke Uchiha has become nearly the opposite of the perfect emotionless shinobi he was once striving to be; he's reckless, disobedient, and so full of rage it completely blinds him to the actions of others (unless they're standing in his way).
In order to get a deeper look at Sasuke personality, and why he does things, we look back at his child hood. His brother Itachi was the genius, the golden boy of the Uchiha clan. Being Itachi's younger brother, Sasuke felt this pressure constantly from all of his friends, family and even himself. At an early age, Sasuke decides he wants to be exactly like Itachi, and do things exactly like Itachi has. Itachi becomes his role model in every way and he would spend as much time as possible with him.
At first, it even seems like his own father is pushing for Sasuke to be more like Itachi. And to seven-year-old Sasuke, it's important to him to please both of his parents. So when it seems like his father is disappointed in his abilities (or lack there of), Sasuke gets slightly down on himself. It's the beginning of his obsession of being perfect, and if not perfect, then being the best. At this time, he doesn't know about all of the cruel politics going on behind the scenes, and isn't aware of how his father actually dislikes his eldest son, and wants Sasuke to be nothing like him. He only wants to be perfect for his father, just like Itachi was.
Despite all of this, Sasuke loved his brother very much, and it seemed Itachi loved his little brother just as much. Itachi would take care of his brother, no matter what. And Sasuke worshiped him as everyone else did because of it, even if Itachi would have to forgo giving him the time he wanted.
When the massacre happened, all of that changed for Sasuke.
Despite being told recently what actually was going on that night, Sasuke only saw one side of it. Sasuke had been returning from school, only to find that all of his family had been killed mercilessly. He got home, and saw Itachi kill their parents. Itachi told Sasuke that he wasn't worth the effort to kill. And that in order to kill him, he needed to hate him. If he didn't hate him, Sasuke would never be strong enough to defeat him. Itachi left the 8-year-old Sasuke alone and broken. Not only was and from then, on Sasuke became an avenger, determined to get stronger and kill his brother.
When he was younger, he merely tolerated his team mates and teacher. Sakura was annoying, but talented, and Naruto was an idiot but tenacious. Kakashi had almost become a father figure to him in some strange way. After leaving Konoha though and being separated from them for so long gave him a completely different stance on them; he didn't care about them. They were a part of his past (even though this current Sasuke seems to hold onto the past as if it's the only thing holding him together...or at least some parts of his past). Even now, he couldn't really give a shit about any of them, except that Naruto had to once again get involved in a situation that didn't concern him.
While Naruto is a complete moron in Sasuke's eyes, he's also an extremely dangerous rival. Part of his reasons for leaving Konoha was that Naruto was getting stronger and stronger each day, while Sasuke felt himself standing still. It wasn't fair. And Sasuke wasn't about to be second best to the idiot of the village. Which is why he fought Naruto in a battle to the death and left the village. Only no one died in that fight. Sasuke insists he let the other live on a whim of his. And now that he's been so skillfully pushed over the edge by his new teacher and last blood relative, he vows that he will kill him. Sasuke knows they will fight one last time, and that's where he'll do what he was supposed to do almost 5 years ago and get rid of the tenacious idiot for good and get the revenge he so desperately needs.
They're all disposable in his eyes. Long gone are the memories of their 'friendships'. He hardly trusts Sakura when she offers her loyalty to him. And is all to willing to kill any of them for standing up to him.
Even with the members of his team 'Taka' are disposable to him. He doesn't blink when he stabs Karin through the chest in order to kill one of the people responsible for his clan's massacre, and hardly remembers the captured Suigetsu and Juugo. Once he may have rescued them. But now all that matters is the blood; the blood of his family. Everyone and everything else have little meaning unless they are a stepping stone to his ultimate goal.
As stated before, hatred was a seed that was planted in Sasuke by Itachi long ago. A seed that was going to be nurtured and sustained only by Itachi until Sasuke was finally able to kill him. For a few moments in his life, Sasuke was free of that hatred. After Itachi's death, Sasuke had sort of fulfilled his duty. While the death was not entirely by his hand, he was the last one standing. If things had gone differently, Sasuke may have been haunted by the fact that he didn't technically defeat Itachi himself; not complete, but left alive without a purpose. He expected to die and didn't expect to have a future, so when suddenly presented one by a thought to be dead relative, he's thrown off.
Thanks to some quick actions by Madara Uchiha, that dying seed of hatred was brought back to life in Sasuke, and its focus was directed to two places; the place he once called home, Konohagakure, and himself.
Madara told Sasuke of Itachi's innocence and of Konoha's orders to Itachi to kill everyone in their clan. Itachi had spared Sasuke because of his love for him.
Sasuke had always had a thing before Itachi's death; he didn't kill anyone. He would injure and incapcitate, but never kill. Because those people were not the ones that wronged. So discovering Itachi's innocence crushed him completely. He had gone against everything he believed in and reinforced in his mind. And that slowly but surely pushes him of the edge and into darkness. He's more quick to anger than he's ever been, lashing out at small things. He's getting less sleep, something told to us by the dark rings under his eyes. He curses more and puts himself in situations where there is no guarantee he'll win. He will kill anyone that stands in his way without mercy.
He truly feels Itachi's death is his fault and it haunts him. He should have realized what Itachi was doing. A hatred stronger He directs this hatred of himself on the ones who did this to Itachi, and the entire village of Konoha for not realizing it sooner.
The place would fuck with his already delicate balance of sanity and insanity. His first few weeks there, he would destroy anything he could get his hands on, his whole motive being 'he has more important things to do.' Somewhere as perfect as Pleasantville should never exist in his mind. The world is too fucked up for perfect little houses, and perfect people being perfect every second of everyday.
It would just continually remind him how imperfect he is. A perfectionist that's imperfect.
He would close off for weeks at a time, only to cause havoc when disturbed be one too many chirping birds singing one too many cheery songs. It would be a never ending loop until he realizes he's been in Pleasantville nearly a year. While he'll never truly give up, he would cage his rage and energy, learning that he should be saving this for whoever placed him in this mess in the first place. So leaving when leaving the perfect little house in the perfect little neighborhood, Sasuke has a new short term goal; kill the god who brought him here and leave as soon as possible.