To argue this fairly, I need to define "exists." I mean something that is real independent of human minds. Under that definition, the burden is on the other side to show why a god is not just an idea or a comfort. But here is my strongest point: every concrete claim about god's action reduces to something natural, like a feeling, a coincidence, or a text written by people. If god were actually there, we'd expect at least one unambiguous, testable effect that only a supernatural being could produce. We have none. So the reasonable conclusion is that god is a concept, not a fact.