Knowing both Parsons and Beversluis, (Parsons through having lived in a house with him when we were both seminary students in the late 70s, Beversluis through correspondence about Lewis), I do find this dismaying.
I would just note that the believer-unbeliever divide is one of the things that divides us most deeply. Being in error about God certainly has a greater impact on who we are than being in error about abstract objects, or counterfactual conditionals. You also have to realize that the atheist philosopher is talking about what he doesn't believe, while the Christian is talking about what he does believe.