First off: I think atheism is probably true. My philosophy teacher actually polled the class and I said that my confidence level that there is no God is 70%. According to atheists like Richard Dawkins that would probably make me an atheist. Yet I consider myself an agnostic mainly because I recognize the fallibility of human reason, particularly my own. All it takes is subtle prejudice or one unexamined premise for things to fall apart. Moreover, the Universe is a mysterious place full of unanswered questions, and that's not a pronouncement I am prepared to make.
I digress. According to atheists like Dawkins and others, atheism is something to be happy about. It is to be embraced. I think the complete human autonomy implied by atheism is appealing--to be able to do absolutely anything you want without having to worry about divine retribution. But I think the negatives outweigh it considerably:
1. If atheism is true, everything and everyone you know and love will perish and die. Hawaiian sunsets, the Louvre, your Grandmother, your friends, your children, are transient, and will be snuffed out of existence. They''ll be no more. They may as well have never existed. The sun is going to explode and the Universe will collapse in on itself. Not exactly a pleasant outlook.
2. Atheism robs our lives of any real, objective, transcendent meaning. We are accidents. Natural selection did not have us in mind. Purpose can only be given by the conscious action of intelligent agents. A watch has a purpose. Art has a purpose. What purpose could milk splattered across the kitchen table have, or a river rock forged over millions of years by hydraulic and geological processes? None of course, and we came about by the same natural processes. Everything is meaningless and pointless.
This? This is what you want?