I recently read "Decadent Society" as part of a binge on what another commenter calls "conservative intellectual" literature of the past couple of years. I'm not sure Douthat really makes a great case for his thesis but there is, to me, a sort of haunting note of truth to it--a sense of your "Fizzle" having entered a feedback loop that is difficult to ascertain from the inside.

Since I did march through the literature binge, I'll add that some conservative authors are quite a bit more pointed in their analyses than is Douthat. "Age of Entitlement," and "Return of the Strong Gods" are two titles that come to mind.