Is it really necessary to get along? There are societal laws that one has to be careful of. Certainly an atheist doesn't want to be a fool and bring society down on himself.
But if the Atheist can gain from violating societal laws and conventions with a reasonable certainty that society will never be the wiser, then does the Atheist believe that it is "wrong" to do so? I would think a true atheist would act entirely in his self interest.
Saddam is a good example of a man who lived like an atheist. He used religion when it suited his needs. He also fed men to the shredder when it suited his needs. He lived totally for himself. And because He did, he became very powerful, which is what he desired.