I think Eugene is right to suggest that Will Smith did not really say that Adolf Hitler was a good person, but merely claimed that Hitler himself believed that he was doing the right thing. The latter is, as far as I know, an uncontroversial statement among experts on Nazi Germany. However, it's striking that so many observers - including the reporter who interviewed Smith and Instapundit - seem to conflate the two.

The confusion is at least in part the result of a shortcoming of the pop culture image of evil. We tend to think of evil people as those who know what they are doing is wrong, but do it anyway. In reality, most of the world's greatest evildoers, Hitler included, actually believe that their evil actions are morally praiseworthy. Many - notably the Nazis, Communists, and today's radical Islamists - have elaborate ideologies that validate those actions. Indeed, it is striking that most of the great mass murders of the last century were committed by Nazi or Commmunist regimes in order to advance their strong ideological and moral commitments. If Lenin, Stalin, Hitler, and Mao had cared only about their narrow self-interest and holding onto power, they would have killed many fewer people. Even serial killers often believe that their actions are justified - either on weird ideological grounds of some kind or as a response to real or imagined slights that they have suffered. In real life, there are very few cackling villains open reveling in (what they admit to be) their evil ways. As Smith said of Hitler, the typical mass murderer "woke up in the morning and using a twisted, backwards logic, . . . set out to do what he thought was 'good'."

We often praise those who seem "principled," are "people of faith," or show other signs of genuine moral commitment. The most dangerous evildoers, however, are not those who lack principles altogether, but those who believe all too fervently in the wrong ones.

UPDATE: I do, however, think that Smith was naive to suggest that Hitler's type of evil could be addressed through "reprogramming," at least not if "reprogramming" simply means education and persuasion. By all accounts, Hitler was strongly committed to his ideology and was unlikely to change his mind about its fundamentals. Of those prominent Nazi leaders taken alive by the Allies at the end of World War II, very few (such as Albert Speer) ever admitted that Nazi ideology was wrong, despite extensive efforts to persuade them to do so.