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

[Mister Agenda]

When I was a theist, it wasn't really argumentation that pushed me away from theism. First it was (apparently ill-advisedly) reading the Bible from front to back. Then I kept finding out that things my fellow Christians were claiming weren't actually true (if I still misunderstood evolution as badly as I did when I was a Christian, I still wouldn't believe it). But that only got me as far as 'not a Christian', not as far as 'not a theist'.

Learning about logic and arguments was an important step, but it wasn't so much that I noticed a good argument for atheism as I noticed all the arguments the theists were using were flawed and didn't actually establish the case they were trying to make. That surprised me. I surveyed arguments for God, trying to find one that stood up to scrutiny. I was left thinking that the only reason to not dismiss ideas of God in total with absolute certainty is that some versions are at least not impossible. I had gone from agnostic theist to 'agnostic agnostic'. It was only later that I was exposed to information about atheists and atheism (I had read The Selfish Gene back in 79, but it was just a book about biology to me and Dawkins hadn't yet become an open advocate for atheism). At that point, I thought the 'weak atheist' label applied to me, and over 20 years later, still do.