-Putting his fist through Naruto's chest. (For a good part of the fight Naruto was trying to do the same but hey.)
-Going AWOL from Konoha.
-Learning techniques from a known enemy of Konoha.
-Killing people. Innocent people, random people, ex-best friends -- hell, even enemies. He doesn't kill.
¤ Orochimaru complains that even in a melee of a bazilion Sound Nins trying their best to shish kebob him, Sasuke finds a way to beat them all without killing a single one. Pretty sure bet that attitude isn't new, most likely he hasn't killed anyone since the Valley of the End.
¤ He doesn't really kill Orochimaru, he absorbs him. [This one is the iffiest because the end result is quite similar and Sasuke did attack first with the intent of dispatching him; but from another angle of view he knew in the end only him or Orochimaru would walk away alive, so it was kind of proactive self-defense. (also Orochimaru is portrayed as a somewhat despicable enemy who apparently doesn't deserve a noble one-on-one. >.>;; That's more of a meta reason than an in-universe reason though.)]
¤ Deidara killed himself; Sasuke just wanted info and would have let him go since he couldn't care less about Deidara as a person.
¤ Doesn't even let Suigetsu kill people -- he could just say "I won't kill, but you can do whatever you want"; instead he takes responsibility for Suigetsu's behavior.
¤ Itachi was terminally sick and knew it when he started the fight; he keeled over from exhaustion.
¤ Killer Bee escaped safe and sound (though I have to believe that Sasuke actually KNEW the Killer Bee they handed over to be de-bijuu'd was a fake, because if he didn't he would only be innocent of murder on a technicality. I just can't see the Sasuke who said he would do it all on his own actually not care that he's grabbing some random (granted, annoying) guy from the street and getting him butchered just to get more power. It wouldn't be consistent with the rest of his pattern of behavior.)
-As far as we can tell, going on bad/warmongering missions for the Sound (maybe he went to pick rose petals for Oro's bed! Or washed truckloads of dishes. Who knows. He didn't go and ninja in the night for Sound supremacy) or giving intel that allowed Orochimaru or Madara to cause harm to Konoha. It would be an important, damning fact, another turn on the downward spiral to ~*darkness*~. If it had happened, we would have seen it in the manga. It's not the kind of thing Kishimoto would spring on us 200 chapters after the fact. Sasuke is meant to be on the bad guys side at first glance but still honorable at a second glance -- Kishi wouldn't add a "but actually he was making evil decisions from the start I just never felt like mentioning it before" on third look, that's just too zigzaggy. He took from Orochimaru -- new jutsu, enhancing drugs, snake summons -- but he doesn't seem to have given anything back, apart from the promise of his body, which he never made good on. (Sasuke, you goddamn cocktease.)
-Getting contaminated by Orochimaru's "Me Me Me" ideology. He's a very justice/revenge based character, always has been, still is, and has stated and acted on his belief that someone who uses and manipulates others just to coast on their stolen strength with no regard for their lives disgusts him. (... isn't it strange how he isn't saying anything about Akatsuki's quest for bijuu then. HMMM.)
-Getting contaminated by Madara's "I didn't get to be Hokage and beloved by my clan so everyone should die but I'll pretend rather transparently it was really only about my little brother" ideology. No, really. Because...
Let's see what kind of precedent there is to the whole "Yeah, Madara-chan, I'm with you 150 percent! Let's kill those evil mean peoples."
Chapter 309; pages 10 to 12:
Naruto: Why don't you get it? Your body is going to be stolen by Orochimaru anytime now!
Sasuke: If that happens, then it happens. You're still quite the kid, Naruto. Revenge means everything to me. As long as I can have my revenge, I could care less what happens to this body, or to the rest of the world for that matter. Let me make it clear for you... For both me and Orochimaru, killing Itachi now would be impossible. But if I am able to accomplish my goals through nothing more than offering my body to Orochimaru, then he can have my life, and my afterlife for that matter.
Turns out he never intended to hand his body over and let anyone else kill Itachi, because it was his duty and he'd never entrust that to an outsider, especially such an amoral one. He probably knew Orochimaru was close enough to hear and he wasn't stupid enough to tell Team Kakashi "aw stop nagging already, he won't get me because I already plan to kill him first." Orochimaru probably suspected it might be the case, but there's a difference between playing with fire and jumping into a volcano with your eyes wide open.
(I like to think Sasuke also lied to team Seven because he wanted to discourage them from risking themselves by coming after him, because he might have to plunge into darkness to reach his goal but there was no reason to drag them along. So far, though there's his thanks/goodbye to Sakura as semi-precedent for the "I'm glad you want to but I don't want you to follow me" but it's more faith than manga-based fact, alas. So far.)
So when Madara is all "And more importantly, I have won Sasuke over" just because Sasuke told him so... ahaha, that's what Oro-chan thought too, honey.
Especially since 1) you never see Sasuke's face and, more importantly, his eyes for the whole page where he's making his speech that he wants to kill all the villagers, pretty big hint he's probably fibbing and 2) when you look at the border of the pages -- black indicates a flashback. That discussion where Sasuke tells Madara he'll destroy Konoha happens after the discussion where he tells his team hawk he'll go after the elders who ordered Itachi to his ignominy, exile, and death.
Who would he have a better reason to lie to? His personal squad, who follow him because... um... Pretty much because they like him / want to see how far he'll go, and just happen to have a couple of errands they might as well run on the way? Who have no reason to give a damn about Konoha one way or another and just joined Akatsuki because he told them to? Or some mysterious clan elder with genocidal thoughts whom Sasuke's beloved older brother boobytrapped Sasuke to kill? Let's also remember he'd just had a flashback comparing his Hawks to Team Seven. Yeah, sorry Madara, I don't think so. What you got was pretty much just lip service.
Considering his behavior all along the series and the fact he's been known to lie convincingly to megalomaniacs when that'll get him closer to things he wants, it's a pretty sure bet Sasuke never intended to destroy Konoha, kill civilians, kill innocents, kill interlopers, or pretty much kill anyone ... but probably the elders who started that mess with his clan and his brother in the first place.
And since the elders and especially Danzou have been depicted as crooked and warmongering? they're as good as gone and if Sasuke is the one who gets to get rid of them then it will be depicted as a well-deserved death. (IF -- they might also get a karmic accidental death/suicide/Madara-Pain killination, who knows, he still has his "no kill" thing and who knows when/if he'll break it. After all killing Itachi was his goal of a lifetime at some point and in the end he didn't get to.)
In real life or in Seinen manga he probably would be executed for treason, but considering the story genre? He does not need to give his life to redeem himself because he has never taken any.
The origin of his new powers does not matter half as much as what he uses those powers for (also apparently all his lightning techniques came from himself and not Orochimaru, anyway.) Kyuubi is a precedent for that -- Kyuubi's power is dark/evil and might be dangerous for Naruto's friends, but he is still expected by Jiraiya and his father to learn to use it for the greater good.
He DID get rid of Orochimaru who has been a thorn in Konoha's side for a while now, as well as (kind of) two Akatsuki.
He had Suigetsu free Orochimaru's prisoners -- for him, in order of importance, that was probably rather secondary to his goal of getting Karin and Juugo's help, but he still did it.
I don't think he's going to get a free pass. He probably needs to risk his life for the village/his old teammates so he'll show his true loyalties and prove himself useful enough be officially forgiven for being AWOL. He probably needs to get a beatdown from Naruto and hopefully Sakura (I'm sure they already forgave him for Naruto's physical wounds and leaving Sakura behind on that bench, but he'd still deserve it for the emotional turmoil he put them through, and besides he wouldn't stop being a stubborn ass otherwise). He probably needs to get damn close to dying to regain sympathetic points...
But in the end he just hasn't accumulated enough bad karma that nothing short of death would redeem him.
Also, Naruto's only been clamoring that he won't become Hokage if he can't save Sasuke, and we all know he'll become Hokage by the end of the manga, no question about it. >___> [/argument]
Team Seven is the team that will get it right -- Team Sannin exploded because Tsunade was too wrapped up in her grief for her brother and lover to care about her teammates and ran away from her responsibilities, and Oro was twisted from the start and likes what he's doing, and Jiraiya gave up on him and never felt afterwards that he measured up to / deserved to be Hokage; and of team Yondaime Rin was ineffectual, Obito realized what Kakashi really was like too late, Kakashi was too arrogant and now there's only Kakashi left. Team Seven will get it right. They'll save Sasuke from his darkness because he's not evil, he's lost; Sakura will protect/support her teammates like Tsunade never did; and Naruto will never give up.