As a writer, I always strive for proper grammar. Like a musician, you need to know how to play the instrument if you want to make good music.
And as an atheist, I do not believe in God, Jesus, Satan, Allah, or Zeus. Yet these are all proper nouns, referring to deities that many hold dear. So, like the Moby Dick or Ishmael, I may not believe they actually existed but I still capitalize them. And you should, too. It is grammatically correct. Grammar Akbar!
As you may have noticed, I did not capitalize atheist. Some might argue that it is a belief system and therefore should be capitalized like the nouns that refer to the followers of other belief systems – such as Christian, Muslim, or Jew. But an atheist is not technically an adherent of a belief system. There is no actual atheism, either. There is not some doctrine held by those who do not believe in any sort of deity. In fact, that term is typically only used by theists who need to force us into some sort of category based upon their own belief system. They can only think of people in terms of their belief system, with their world clouded by their own religious views, so they assume that we are a religion of non-belief – or perhaps even anti-God. And, in fairness, there is a strain of militant atheist who act like it’s some sort of religion. Though I imagine a lot of it is just good clean fun, like my friend who insists that his mother is a devout atheist, because she doesn’t go to church every Sunday. Atheist Akbar!