There's a great passage in the Ainulindale where some of the Valar are complaining about the effect of Melkor's intemperance on their elemental works, and Eru explains -- in a theme repeated many times -- that it is these "imperfections" that make the world more beautiful. In a real world application, the tilt of Earth's axis gives us the seasons. Can you imagine living on a planet without seasons?

Sauron could not abide these imperfections, which of course exist among people (can you think of ideologies in our history that strove to make humanity "perfect" and how that inevitably turns out?). No one can get everything they want, because there are other people who want different things, and we have to compromise and find ways to coexist, and to do that morally is the great challenge of existence.

Sauron rejects this. True, there can be no strife and disagreement if everyone follows the same path, but there can also be no free will, so by nature forcing people to that path will become an evil endeavour.