I used to be one of those militant atheists that Magister Nemo discusses in his essay, but these days I have a different view. Spiritual religions aren't just based on believing that a god or gods exist. They are based on the belief that there is some all powerful creator, and that creator has (moral) standards that he expects us to live by.
Now, I can't prove that there isn't a god somewhere, no one has the means to search the entire universe. But knowing the age of the universe is reckoned in billions of years and the size of it is simply unimaginable, I can be pretty certain that if there is a god he is not going to give a shit what I do with my genitals, what food I eat or what I do or don't do on certain days of the week. In other words, the question of the existence or non-existence of god (as worshipped by the theists) is irrelevant to my life, the only god I need be concerned by is the one I see when I look in the mirror