In shamanic traditions, there is the notion of ‘creating entities’ inside oneself. These ‘entities’ are either transmitted through education, society etc or created by oneself, consciously or not. During the twentieth century, C.G. Jung created the notion of archetypes, which is an occidental version of the same idea. His ideas around archetypes are absolutely brilliant. To make it short, they are ideas which exert a direct influence on us, well beyond the rational, cerebral realms of our existence, to the point that they can be considered as living, independent beings.
We have a lot of these entities or archetypes in ourself, and it’s them who regulate our inner life and our systems of belief. They will lead us to enjoy a decent, peaceful life, or on the contrary, in extreme cases, to blow ourselves up, together with twenty other people. They will lead us to like some aspects of life, and to strongly dislike others. They will lead us to waging war, to be passionate about a football team, or to create a brilliant piece of writing.
The interesting question is: are these entities real or not? If you approach the question from a logical, external point of view, the answer will be an obvious no. They are imaginary and have no reality. You can’t prove their existence.
And yet, we are heavily influenced by all kinds of archetypes. Why is that? If they had no existence, surely they couldn’t affect us in the way they do? For instance, Jesus or Buddha, or rather what they represent for each of us, are living entities inside of us and influence us in an impressive way, whether we believe in them or not. Influential artists and pieces of art, writers, politicians, scientists, saints enter inside our inner space and exert a huge influence on us, whether they are dead or alive. You can’t count all the artists past and present describing how they have been directly influenced by a spirit or a demon, the writers who say that at times, they just have to sit down at a table with a pen and sheets of paper, and to write down what is dictated to them. What are these entities, these demons, these spirits?
To come back to the thread’s topic, when someone lets the idea of God enter inside, it becomes a living entity as well, and can be directly experienced. The question is, is it our freely chosen version of God, or one which is imposed on us by a church or a religion? It’s really up to us to make this choice.
Of course, it’s also possible to reject the idea of God. In that case, there is no entity representing God, the archetype called God exerts no influence at all. It does literally not exist.
The logical conclusion is thus: when an atheist says that God doesn’t exist, he’s 100% right, no discussion there. And when someone has regular contact with a loving and lenient deity he choses to call God, his experience has full validity as well. Proof isn’t necessary, the experience can be made by anyone opening his or her mind. Isn’t that great? 
That’s also why the idea of atheism, once accepted, is a hugely freeing one for all people who have been previously dominated by a tyrannic, jealous and cruel entity called God (to take Klopptimist’s words). And let’s admit it, the idea of God as imposed on us from the outside (church, family, society etc.) is, at least in part, terrifying. Atheism is a good way to free oneself of a pre-conceived idea of God, it’s basically making tabula rasa of all the old, outdated ideas clogging up our inner space. It’s a positive thing in my book.
Once that space is freed up though, is atheism the be all and end all for all eternity? I for one try to create inside of myself an idea of God as I would like it to be, in the knowledge that it will progressively start to exist, and exert its influence on me, like a virtuous cycle.
But that’s obviously for everyone to decide for him/herself. I completely respect the atheist position, as well as those who chose to freely nurture the idea of a loving God as they have received it from their parents for instance.
An idea I can really relate to, and am thus willing to let enter my inner space, is the one wonderfully formulated by Rilke in many of his poems, that God is essentially a work under construction, and by no means the finished product yet.
