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

[SteveII]

You mean there are other alternatives to consider? What? 

If you are going to say the Multiverse, then you have just pushed back the problem. If order for any multiverse to spawn billions upon billions of universes--each unique in its physical laws and constants, doesn't it too have to be fine-tuned to do so?

According to your argument God would have to be finely tuned as well, and to reject this is committing the fallacy of special pleading. God is just another candidate hypothesis to the solution of the fine tuning problem (if it even exists), and this hypothesis doesn't magically get a free pass.

I'll grant God is finely tuned to create universes. You are making a category error. You want to believe there is a naturalistic explanation against all odds. I believe there is a personal (intentional design) explanation. If you stick with the naturalistic, and propose a multiverse, you are only doing so to explain away the odds but really you have just moved the same problem back one step.  BTW, you have also crossed from science and entered the realm of metaphysics--because there is nothing scientific about a multiverse.