Many non-believers genuinely explain that their non-believing comes from the simple fact that they do not have a proof that God exists. And behaving without proof seems to be the most reprehensible sort of act that a man can do. What can you give as a proof of God if you are a believer? Blaise Pascal wrote that God was not a geometrical problem, and that you could not give it a solution. Part of the supposed impossibilities comes from the fact that what you would use to prove God would be biased in any way, and thus not objective proof. Biased by what? By God! If by "God" you mean the kind of God I refer to here, then whatever we know in existence, tools of measures, arguments, logic, etc., all of these are either of God, or God, or from God, or by God. There is no escaping His presence in whatever means you ask of believers to use to prove God. It amounts to proving that you can see with your eye itself. Sure enough you can see, but without resorting to something other than your eye, you will have a hard time proving it. With God, this becomes impossible, perhaps, because God comprehends the whole of the little of the reality we know.
Now, to the funny side of things. Those people who refuse to even consider using their imagination to think of a world with a God simply because there is "no proof" actually are extremely faithful to certain dogmas, which they don't so much as question. Sex with your parents would be one of those things. I would love to ask someone who refuses to think about God why they refuse to have sex with their parents, and why they think it is an abomination (a feeling I too share, just so you don't get freaked out on me). What is the proof that sex with your mother or father (or mother and father) is a bad thing? Let's see what usually comes up to that question.
"It makes monstrous children!" That is a funny one; as if you'd never think of wearing a condom when you do your mother; as if you couldn't blow your dad. That argument is thus out, and if you resort to it, you're only using a pale excuse of a reason, because there is no rational reason in this.
"It is immoral!" And sure enough, I agree with this, but the interesting thing here is to try to understand why that is. I don't think anyone can come up with a good reason. Sociologists tried, anthropologists tried. Some thought that it was an inherent instinct in us, which strove to force us to diversify our blood and genes so that we would not remain in a constrained pool of chromosomes but have all the riches available. Problem is that this "instinct" doesn't seem to work every time. Many societies didn't heed much those incestuous problems, and Man has been known to marry his mother and be the father of his siblings. So the instinct argument is out too.
What's left? Certainly other arguments I either forget or know not. But the point is the following: you don't need a proof to know that sexing your parents is a bad thing. Are you right? You can't prove it, but you're damn sure of it. And no matter how skeptical I am, and how aware that I have no rational reason not to sex my parents, I will never do it. Here is something I need no explanation for.
I consider it quite possible that some, or many, or most, believers who feel they have faith and who feel God - and that will always be a great mystery to me - experience a knowledge of that category, perhaps. They have no proof, but it makes little difference. Unlike any other thing we know in this universe, God does not belong there the way we do. He's either wholly outside of the created universe, or immanent to it, or both, or neither; these speculations, for the most part, lay beyond human comprehension, and all we can do is talk about it.
In our time, people love to decompose things, analyse them, deconstruct, see what's inside of their dolls and how things work, but they also tend to think that this is enough to understand the world, and that indeed, this world can be understood. Every mystic and most spiritual people know otherwise. It is merely being humble to admit that most things are quite beyond us. But it is that reflex in today's human that prompts him or her to ask God to be undone into a set of smaller elements, so that a good autopsy can be performed, and that we finally get to understand God. That cannot be done, no more than the stage actor can tell his audience he is but an actor without killing the willing suspension of disbelief. As C.S. Lewis said, as soon as the playwright walks upon the stage, the play is over. The same probably holds true for God.
If there is a God, and He fits what we usually consider Him to be, then He must necessarily take all the room. I am not even trying to consider in what way that would be done, transcendentally or immanently, but directly or indirectly, God would be everywhere, in whatever substance or lack thereof. An omnipotent being, and an omniscient one at that, would necessarily be everywhere, and could be anywhere, which amounts to the same.
So the mystery remains. For us to decompose God into smaller elements that we can comprehend we would have to be more than God, which, in theory, is impossible. You are asking the ant to suddenly step up a bit, study biology at a university nearby for seven years, and then analyse its peers. Peers! To analyse God is like being ants trying to analyse the innards of a computer, which most of us can't even make function properly. The task is too daunting to be considered, though we should still try, just with the awareness of being little humble ants who don't know all that much.
This is one thing I like about religions: they don't claim to understand everything very well. All great religions are based on revelations, not explanations, since you can't explain everything to finite beings. Of course, to the skeptic and slightly negative mind, this will sound like an easy way out. I am not refusing to endeavour to explain, I merely explain that there is no explanation to be given, not the kind that you ask for. And if you insist, please come back with a striking explanation of why sex with our parents is a thing we all hate to even think of, while none of us has a good reason not to do it except the disgust itself.