This book very obviously demonstrates the two polar opposites of good and evil: Harry is good, and Voldemort is evil. But while the book demonstrates this theme very clearly, I don't entirely agree with it. Yes, I think Voldemort is evil, but I don't think the Death Eaters are. While the Death Eaters have done evil things, what I think is most important is what drives them to do what they do.
I find to be very easy to pinpoint the Death Eaters as evil people without giving much thought to it. They have committed many evil deeds, deeds that virtually cannot be forgiven. They are the followers of true evil. But how much of their lifestyle was their choice? When Voldemort first came to power, before Harry was even born, the people of the wizarding world only had two choices: you either had to be with him, or against him. I can see why the Death Eaters thought that to ally with Voldemort was safer way to go. It was the safer choice, but it was not the right choice. The Death Eaters are not evil for siding with Voldemort. The only thing that the Death Eaters really are are cowards.
In retrospect, though, being a Death Eater is not that safe either. If any Death Eater does not carry out what Voldemort has wished, they do face certain death. That is why I believe that it is fear that is the true root of the Death Eater's actions, not evil. They fear death. Fear of death is why they commit those evil deeds. Fear of death is why they joined Voldemort in the first place. They were afraid of Voldemort, and they still are afraid of Voldemort. But when you look back even further, it turns out that if Voldemort did not fear death, he never would have became who he was. So is it fear of death that drives people to do evil things? And does doing evil things automatically make someone evil?