The core question is whether God exists. Atheists think the answer is no. We have pretty good evidence that tells us God is very improbable, if not impossible. This evidence comes from many fields, from biology and cosmology to archaeology and paleography. God is also totally irrelevant to morality. There's no law and no prohibition that requires - requires, I say - the authority of a God.
The God idea offers so little. Yes, it makes some people feel like they have a personal connection with the universe. Yes, it helps some people think through their moral choices and their standards. But it's not true. God is a tool, and that's all. God should not be made into a mental idol.
Atheists totally reject idolatry. In this regard and many others we are the better Jews.
So many Jews become agnostic and atheist. So many intermarry. Why is this? Because they learn to be independent thinkers and to ask questions, such as where the Torah and its commentaries come from. When one looks, it becomes pretty clear (1) that the Bible is man made, and (2) that God is utterly unnecessary.
I'm OK with this. So what that the Torah isn't divine? So what that God doesn't exist? So what that Moses never led 3 million slaves through the sea? So what that there's no messiah? So what that there's no afterlife?
It doesn't matter. It really changes nothing. It makes us no different than before. It has no bearing on the past or the future.
Outside of ancient books and commentary, what is the evidence for theism? Where is it? Isn't there even one single fact of physical reality that would independently verify a claim for existence of god, the devil, heaven, giants, ghosts, golems and so on? Where's the frackin' evidence? Or do people just want to decide such matters based on personal feelings of awe when looking at a sunrise?
Proponents of intelligent design always carp that evolutionists and materialists rule out the possibility of divine intervention from the beginning. But what exactly is the reason we should ever rule it in? They seemingly assume that a supernatural explanation is legitimate prima facie. But I disagree, and I think most atheists do too. This is why the burden of proof is on the theist. They are saying there's a dragon in the garage. That's fine, but don't force others to accept the statement as true unless you have the means to support it independently.