"OK, I can't prove God exists, but you can't prove He doesn't."
The implication, of course, is that the conversation is now on even ground. But there is a fundamental difference between these two views: I can't prove God doesn't exist, because it is a logical impossibility, you can't prove He does, because you lack the evidence.
Logically speaking, the existence of God is provable. So if He really exists, why can't anyone prove it?