Atheism = "true" by convention?

I listened to the Bahnsen v. Stein debate (audio here / transcript here) again and caught something pivotal in it I had missed before. You'll recall that Dr. Bahnsen went hard after Dr. Stein concerning the laws of logic and whether an atheist could make sense out of them given their materialist/naturalist worldview. Dr. Stein said that he believed the laws of logic were a convention:

Bahnsen: Do you believe there are laws of logic then?
Stein: Absolutely.
Bahnsen: Are they universal?
Stein: They are agreed upon by human beings not realizing it is just out in nature.
Bahnsen: Are they simply conventions then?
Stein: They are conventions that are self-verifying.
Bahnsen: Are they sociological laws or laws of thought?
Stein: They are laws of thought which are interpreted by man.

Later in Bahnsen's remarks he rightly exposed Stein's atheist worldview as having no basis for rationality since for Stein the laws of logic (by which Stein purportedly made truth judgements) were simply a matter of convention -- the logical consequence being that Stein's atheism was a matter of convention. Stein insisted he was being "rational" and that Christianity was "irrational" but he certainly did not want to admit that those comments were based on convention. Bahnsen went on to demonstrate that in the Christian wordlview the laws of logic are not conventional but rather that they are universal, invariant, and abstract -- that is, they are truly laws rather than just agreed upon by people.

What I want you to notice is that Stein unwittingly admitted defeat in the debate during the first cross examination. Check it out:

Stein: Dr. Bahnsen, would you call God material or immaterial?
Bahnsen: Immaterial.
Stein: What is something that's immaterial?
Bahnsen: Something not extended in space.
Stein: Can you give me any other example, other than God, that's immaterial?
Bahnsen: The laws of logic.
Stein: Are we putting God as an equivalent thing to the laws of logic?
Bahnsen: No, only if you think all factual questions are answered in the very same way would you even assume that by thinking that there are two immaterial things that they must be identical....
Stein: I not assuming that. I'm just assuming that because the laws of logic are conventions among men. Are you saying that God is a convention among men?
Bahnsen: I don't accept the claim that the laws of logic - that Christ's laws of logic - are conventional.

What I want you to notice is brought out it greater clarity in the audio verson, but can you see what I'm getting at? Stein wanted to argue that God is just a convention of men! In other words, you can't say for certain that God exists because He's just a convention of men! After all, conventions can't be trusted for certain! And yet Stein openly admitted that his own belief about the laws of logic is that they are a convention! See? The atheist Stein wants to reason about God using laws of logic that he says are conventional, then he turns around and ridicules convention! Stein admits his own defeat.