Theists: What is the most compelling argument you have heard for Atheism?

[Brian37]

Right.  No conflict with science at all.

Steve II already provided the standard dodge to this and every other perfectly good example you can provide: the cause is allegedly supernatural and therefore outside the purview of scientific inquiry and judgement.

Of course, it's all bullshit designed to avoid admitting one's religious stories are silly and antiquated. Reasoning with such people is largely a waste of time.

No unfortunately it is not a waste of time. Problem is religion gets peddled mostly to children before they can formulate adult critical thinking skills and in greater numbers that ends up competing at a political and global level and that in turn can affect you even when you don't want it to.

It is still important to read the history of as much of the world's religious history so that you can call out the bad logic. It is also still important so that other skeptics can view arguments they may not have considered. I can tell you when I first identified my position as "atheist" I was very ignorant 17 years ago compared to today. Having seen the posts of other atheists lead me to read more from scientists and other atheists. 

You cant force any religion out of existence, no, but ignoring it is foolish too. I think it is very important to have these websites and debates, not about winning a game but about exposing more to the value of questioning and skepticism. It is harder to indoctrinate someone when they are well armed. Theists often come in here thinking falsely that we are lost puppies to be saved. Many are shocked when we dont simply say "That sounds great, where do I join up?".