Harry approached Quirrell when he was only eleven years old...and was faced with a viewpoint that a child at such an age would not be expected to understand. Quirrell said that Voldemort showed him that there was no good or evil, only power, and those too weak to seek it.
It is difficult to imagine that the universe only consists of binaries- black and white, God and Satan. There is color with shades of gray, layers upon layers of intricate complexities that cannot be seen all at once. Voldemort, of course, uses these complexities to justify his actions, but others in reality have done the same. Hitler, Pol Pot, and other dictators, mass murderers, and terrorists probably never considered their actions evil- which bodes the thought that it is the 'weak' the victims of the crimes in whatever shape or form, who label good and evil, and it is the powerful who, instead, define right and wrong. So was Quirrell right? Is there no good or evil- just the weak and the strong? And what does that mean for those trying to make a difference in the world?
I think he was both right and wrong. There's a spectrum of good and evil and a spectrum of powerful and weak. Everyone wants power, but not everyone actively seeks it.
For some people, power looks like control over themselves or social acceptance, for some people it looks like world domination or whatever. It's still a FORM of power that they're looking for, even though they don't necessarily see it that way.
But are power and goodness necessarily opposites? I don't think so. I think that people who are too weak to actively seek power can still be evil, or at least on the more evil side of the spectrum. We think of power-hungry people as being evil, and sure rape is about power and Voldemort or Hitler wanted power, but I'm sure there are people out there who would go out and do those evil things if they had the guts. So having the guts isn't necessarily good.
I think that I'm not making sense right now. What I'm trying to say is this: there is power and those too weak to seek it, but there are also good and evil. It's just that most things are, like, a 9.8 on the evilometer instead of a 10, but that doesn't make them good.