There are very few pure evil characters in Naruto. Some are Orochimaru, Hidan, Madara and Obito.
Most of the others became "evil" because of their circumstances and must of those go back to being good in the end, like Zabuza, Pain, and Sasuke. It's only realistic in a world like Naruto for some characters to become evil. I've never understood why these characters, especially Sasuke are so hated. They are confused and live in a violent world. Of course, they will respond violently. They are only flawed humans. Not everybody is Naruto and stays good no matter what.
Many of the characters on the heroes' side aren't heroes, like Danzo and Itachi. Both had to do evil things like genocide but remained on the good side. these two characters could very easily be villains if the hero was on a different side.
Naruto however is, of course, the good guy. Despite having a darker backstory than most of the "villains," he has never been tempted by evil. I've always found this somewhat annoying. If you have a dark backstory, you will lapse into evil unless your name is Naruto or Kakashi.
h i getchya. But as i said in my earlier post he thinks this is his justice. would you call Pain a bloodthirsty villian just cause he tried to achieve peace his way? Obito doesn't care who he kills because he thinks he can revive them in the infinite tsukyomi. People like Orochimaru who experiment and kill people for fun have no intention on bringing them back or achieving peace
