On what other basis might a believer and a non-believer discuss the question?
The common thing between both believer and non-believer is believing.
believing, believing, believing, but not Sure.
Believer = the one who believe in the existence of God. But not yet sure.
Non-believer = the one who doesn't-believe in the existence of God. But not yet sure.
Both believer and non-believer are on the same boat. The only difference is that one is standing in the front and other one on the rear.
Like; the one believe there are dolphins ahead in the sea is standing at the front, but the another-one who don't is standing at the rear. Both believe, but NOT-Sure.
One becomes believer, or a non-believer POST-Discussion, Not PRE-Discussion.
Therefore, there's no need of any more discussion after POST-Discussion.
Any discussion after POST-Discussion will only lead to a fight, rather a discussion.