Many people fail to understand his character development; sure, he turned out sociopath. His goal in the end was puerile. But when Death Note started, he wasn't the main villain. It was when Raito explicitly met Misa when he fell to madness. Yagami is very much a victim of himself. Throughout the series, his own negative qualities prevented him from being truly successful in his goals. I believe that the very core of his aims at the beginning of the series - that is, the desire to make the world a better place by eliminating criminals - was not evil in nature. However, his own arrogance quickly warped that sort-of noble goal into a wicked desire to rule as a god.
Personally, I cannot understand how anyone could reach such an reprehensible conclusion about this character. Although it seems clear that Light did not view himself as an 'evil' person and acted like a god, this detail is irrelevant in determining the morality of his actions. To judge his morality, the question is was he aware of this big positive effect he ended up making in the world, and he was. He planned it from the start and all his assessments on how it would affect the society were absolutely right.
Regardless what anyone says, anyone can prove his methods wrong, but no one can prove his cause the same as well. We live in a society where justice is hard to be explained, as well as evil. Light Yagami certainly was not purely evil nor was his cause purely good. What Nate (N, Near) said about his character to be a sadistic murderer wasn't completely right.
