Barking Up the Wrong Tree has a post, on a study which asked whether power makes us dehumanize people. The answer is "yes". Whether it's childhood bullying, or soldiers and civilians, the wealthy and the poor, whenever there's an imbalance of power it's going to be abused. Not always, but enough of the time any moral person should be concerned and work to change the situation.
[Updated: On second thought, that might be my definition of the difference between conservatism and liberalism: liberalism thinks governmental action can be rational and improve balances of power; conservatism thinks government action will mostly make things worse.]