It's hard to see why anyone would think that believing in a deity is simpler than not. After all, belief in the Christian God carries within it the fundamental problem of why, if God is all-good, all-powerful and acts in the world, evil exists. Theists have been twisting themselves into knots throughout history trying to develop theodicies that explain or vindicate this God. The problem is, every single one of these theodicies depends on some form of special pleading which any half-way competent philosopher can see through easily.I'm asking how it's simpler when atheists often put far more consideration into their position than theists, as well as having to defend themselves far more frequently than theists. They don't have a book telling what to do and what is moral, so they must consider a variety of sources and consider their actions independent of such an absolute source telling them what to do. I don't see how this is simpler.
So Christians and Muslims (and perhaps Jews, not so sure there) have to bear with this very real cognitive dissonance -- usually by ignoring it or pretending it isn't there. Theologians, after all, don't explain their theodicies to congregations. The job of the clergy isn't to confuse the poor sheep, but comfort them, assure them that everything's all right with the world, so they'll come back with their collection plate money next week.
Atheists don't have to worry about this at all. If we assume that there's no god, and that everything is natural, there's nothing to explain. It's often not nice, but it's not a conundrum!