I don't think Douthat's concept of hell is
"gun to the head" morality, it's about everyone else being punished for being naughty, and him getting the grand reward for being nice. He doesn't emphasize hell as something we should believe in to prompt us to do the right thing, he just needs to know that someone is keeping record of all of the times he rejected Chunky Reese Witherspoon's advances and rewards him accordingly.