A lack of a belief in morals by some person or God external to yourself fails as a moral system. If you chose your own set of rules for 'right' and 'wrong', in the first place you would be biased. Either a God (or some similar concept) or an authority whom can excercize power over your actions by some edict would have to exist. You can't be your own judge, because you will always be biased,
thinking yourself better than you are and thinking that you do no wrong.
If you 'elect yourself' to be the rule maker and judge, it would not be impossible for a Hitler, a Saddam, or someone similar to believe that what they were doing was good and not harm. They may 'yes man' themselve to commit any crime. Obviously, a person could also make choices which are 'good', and would fight a Saddam, because whatever criteria you use, 'wrong is wrong', and 'right is right'. You might also choose to have no standards.
Religion does not make a man moral because there are established sins which one is not suppose follow the teachings of the faith. How you act is (usually)
your willful choice. There is no such thing as "Because I am a Christian, I am a rightous man in all that I think and all that I do". A "God complex" is not exlusive to any one faith, any thiest, athiest, agnostic...
To anyone who does not believe a supreme being or a God, what is the source of standands by which to life? Whatever makes you feel happy at the time? Suppose murder made you feel happy? This is not to say that in reality people who do not believe in morals (which has to include punishment should you break them) WILL act imorally (not all drug pushers are Wiccan, nor are Drug Dealers Drug Dealers because of Wicca) - or pagans - or athiests - or Christian - or Jews - etc..