If anyone hasn't seen Dark Knight, it is a great movie. Heath Ledger was an awesome Joker and Christian Bale is the best batman (at least since Val Kilmer?)
One thing that struck me about Dark Knight was how the Joker was always trying to make the Old Adam in people come out in full force. Everything the joker did he would attempt bring out the worst in people: selfishness, pride, anger, and violence. He would give them choices that would test people in their ethics and their feelings toward each other.
However, the show also did give an argument for the natural knowledge of the Law. When people were presented with options to whip each other out, they resisted because they knew something was wrong with it, although they did not know why.
God tell us that the Law is written on our heart by Him. We know that to kill our neighbor is wrong, we know that stealing is wrong, we know sexual relations outside of marriage is wrong, and although we go against the 10 commandments, we all feel a certain amount of guilt (some more than others) And when push comes to shove, often people want to do what is right.
Yet, the darkness will always be with us. As the Joker will always be against Batman, the devil will always be in battle with us and God until the final judgment. Until then, remember your Baptism, cling to the cross, go to worship each week, and receive the Sacrament.