One that's always resonated with me is "People should not be afraid of their governments. Governments should be afraid of their people." from the film adaptation of V for Vendetta.
Another one, from Neil Gaiman's American Gods:
"There's never been a true war that wasn't fought between two sets of people who were certain they were in the right. The really dangerous people believe they are doing whatever they are doing solely and only because it is without question the right thing to do. And that is what makes them dangerous."
Another from Gaiman, in The Sandman:
"Everybody has a secret world inside of them. All of the people of the world, I mean everybody. No matter how dull and boring they are on the outside, inside them they've all got unimaginable, magnificent, wonderful, stupid, amazing worlds. Not just one world. Hundreds of them. Thousands maybe."