Don't you get it? If think your life is worthless, then I can't be wrong in your system. So what if you think otherwise, I have my own subjective view and I can't be wrong. On what basis am I wrong? Is morality observed? Can you observe the proposition that objective right and wrong exist? You are seriously confused.
And why do you not think this happens? Why do you think people don't kill at will? Because MAN has created LAWS using REASON and LOGIC. People that break those laws are considered evil, by rational men. God doesn't come down and support his own absolute laws with punishment for the murder of innocent people. What good does it do to bring Him into the picture on this? It is a weak argument to say that there must be a God to have a civil and free society.