Atheism is the non-belief of any supernatural creating force, deism (my current persuasion, which I am open to debate) is the belief that there has to be a supernatural force behind the universe's creation, as a way of explaining what is currently beyond the reach of science, and most probably will be beyond science's reach for the span of our lifetimes. Theism believes that that supernatural force has a link with humanity on earth, which is not based on reason, but faith, which also provides an instant, convenient, although not necessarily true, answer to man's most important questions: "What is the purpose of living?", "What happens when I die?" and "How did everything come to be as it is today?" The last question is currently being answered by science in the form of evolution and the big bang theory, which puts Theism under a huge amount of stress. Atheists, agnostics, deists and the like are therefore a brave bunch of people, who put the truth before everything else, even at the cost of happiness and content.
As long as I have a mind that can reason, I can't see how I can ever revert back to Theism, even if a large part of me wants to just in order to live forever in a place where the streets are paved with gold.