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

[Mister Agenda]

Strong fine-tuning is a thought experiment in a universe where it's not even known that the constants involved could have been different, that they aren't interrelated, etc. We're not in the position of being able to declare the odds are long...we don't even know if there is more than one 'lottery ticket', or if there are lots with the same numbers on them. We can only speculate.

Can you share a link by a physicist/cosmologist that  discusses the universe's initial constants could have been a large range of values and still been life-permitting? Everything I have ever read says the opposite: https://en.wikipedia.org/wiki/Fine-tuned...e#Examples.

Maybe they can be a wide range of values. Maybe they can't. No one knows. We don't know why the values couldn't have been anything at all (though there's highly suggestive math that a universe with an energy budget at or near zero, which may be all possible universes that can come from a 'big bang' would have a very constrained range of constants) and we don't know they could. How about you find a cosmologist willing to say they know the values could have been different and by how much?

Reread your Wikipedia link and pay attention to all the 'ifs'. If the constants could have been different, there's still problems with jumping to conclusions about why they aren't, but it has not been established that they could have been different, it's only been established that if they were slightly different in certain ways life as we know it would be impossible. It hasn't been established that the constants were random.

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Your fragility of life point does more to support the theist who thinks that God created the entire universe for us than it does as an argument against God.

What need does an omnipotent being have to house its creatures in a hospitable environment? Couldn't God have made us perfectly happy living on the sun or in space by simple fiat?

Solar scientist: How can we live on the sun like this, our bodies should instantly vaporize?
Solar theist: Tis the will of Yahweh!
Solar scientist: I guess it must be something like that, we can't possibly have naturally developed in this environment.

Your version of God seems to have chosen to create the only type of universe where he isn't required to explain the presence of life as we know it.

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No, more like:

1. The fine-tuning of the universe is due to either physical necessity, chance, or design.

2. The fine-tuning of the universe is not due to physical necessity or chance.

3. Therefore, the fine-tuning of the universe is due to design.

Before you jump on any of these, remember that the argument is an inductive argument: in which the premises are viewed as supplying strong evidence for the truth of the conclusion.

2. Mere assertion.

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I never addressed necessity. My understanding is that the laws of physics do not dictate the constants we are discussing, so they each could have been different over a fairly wide range.  Therefore they are not the way they are due to necessity. 

In your version, you would need to have reasons why design as less likely than the others.

Your syllogism declares that the apparent fine-tuning of the universe to permit life is not due to necessity. You seem to have different standards for 'never addressed' than I do.