We don't stop believing in Santa Claus because we realize he doesn't exist. We stop believing in Santa because we realize others don't believe he exists. In life, there's the stuff we can pretty much all agree on. The sun gives off light. If you throw something in the air, it falls to the ground. The earth is round. We grow old. We die. There is no Santa Claus.
A lot of really great stuff can be done with all this common knowledge. We can build buildings, fly airplanes, avoid poisonous fruit, come in out of the rain. Why, we've even learned the rain isn't personal
"Religion serves a good purpose, right?"
Then there's the stuff we can't agree on. The biggest of which being: what happens after death. We humans just don't know. Yet religion is based on answering this question and others that are equally unknowable and unprovable.
In today's world, were a new idea to circulate with religion's accreditation, it would be taken as 
seriously as the latest psychic hot-line or star-bound cult. But because religion has been rooted in our brains since Early Man's first panic attack, it's going to be a long, long time before God becomes socially demoted to the same status as your basic daily horoscope.
In the meantime, religion serves a good purpose, right? Not if you take into account the views of two different authors who object to this notion at great risk to their personal safety. (If a truly religious person believes in their religion, why not let God take care of it?)
The End of Faith by Sam Harris and God Is Not Great by Christopher Hitchens are firm in their assertion that the gods are wearing no clothes.
Their argument in my nutshell: We've come way too far to still believe in the hearsay of ancients. Moreover, the world would be a better, calmer, saner, more peaceful, more functional place if we only stick to the stuff we can all agree on. That is to say, if the only acceptable behavior is acting on that which we can all see, hear, touch and experience right before our eyes. 
Like math. And gravity. And anything that can be tested and replicated over time by anyone, more or less.
Example: If you inhale and exhale, you have a better shot at staying alive. Everyone agree? Great, let's keep living.
However, if you have a belief about what happens after someone stops breathing forever (and you base your entire life on that unknowable, unprovable, unreasonable belief), stop right there. You have just been deemed a danger and a threat to society, like anyone who acts on behalf of their invisible friend(s).
To someone who doesn't believe in Santa Claus, that's the end of the argument about god, greatness and faith.
