This is a very helpful post from Goldblog:
Are cops aware of the immense power they have? The power to arrest someone is awesome; any cop, at any moment, can take temporarily take your freedom. Yes, there are courts to protect the rights of the innocent, but in the meantime, a police officer can still put handcuffs on you, shove you in the back of his vehicle, fingerprint you and lock you up for at least a couple of hours; and lock you up with some pretty mangy people if he so desires. That is real power, traumatizing power. Society grants police officers that power, but in exchange, we must expect certain things -- that the police officer granted this responsibility show more patience, more kindness, and better judgment than the average citizen.
The best cops would not, I suspect, disagree. But even the best cops have bad days. And it's always safer to be Harold than Kumar.