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

[Pat Mustard]

3. The universe's existence and fine tuning being a brute fact is not simplicity. It defies all reasoning with no explanation (or hope of one). That does not sit well with most people.

You're mistaking an effect for a cause. The universe isnt the way it is to accomodate the exisetence of humanity (as evidenced by the fact that 99.9% of the universe is hostile to humanity), but we exist because the universe is the way it is.