I can't really top what Nyu said, but...
He's right.
It's subjective, really. Considering the Black and White craze sweeping everywhere, I'll use N as an example.
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He was simply pursuing his ideals, the ideas that he was brought up with and lived with; He saw nothing wrong with what he was doing and was intent on making the future he saw a reality. Was he wrong? Maybe, who can say? Maybe he was right. Liberating Pokemon from their captivity under trainers... Is that so bad? And was he wrong in doing what he wanted? I sure don't think so. And in the end, with the city with the 8th gym, after Ghetsis' rally, people started to question: "Is he really a hero?" "Is this really what's for the best?" etc etc [s]sue me, I've already forgotten[/s]
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So sure, there could be a such thing a "good" and "evil", no doubt.
But who draws the line?
That's my view on it.