The happiness of false hope

Christians can be charitable and kind towards others by believing that their actions have greater spiritual meaning.  Mormons can be excessively good natured towards people, as in the South Park episode that compares how cynical normal people are.  Buddhism and Hinduism both emphasize good actions over bad actions.  Someone like Stephen Colbert who can recognize hypocrisy and contradiction still has faith in a God, teaches Sunday school, and maintains an upbeat attitude.  If all of these people realized that that there is no God, no afterlife, no spirit, no spirituality, and all religion is a set of myths and lies, then how would they act? 

I'm sure a lot would cynical, negative, and ill natured towards others.  Why be nice to others if there's no universal scorekeeper?  No reward for your good deeds?  In fact, you'll probably get taken advantage of.  Ayn Rand describes this well, advocating Egoism rather than allowing yourself to be manipulated and taken advantage of due to the appeasing, subservient attitude that most religions bring.

So without religion could people still be as happy, as generous, as charitable as they are now?  Or would a larger number be more selfish and self centered than they are now?  Is it better to have a negative but truthful society, or a happy society built on lies?

The defining factor between good and evil isn't religion.