I disagree. Even when you look at the short term view Keynes had, there are very clear losses in waiting for the market to return to equilibrium. Having an economy operating under potential capacity will result in less output than if it ran at full capacity. It's perfectly straightforward - idle labour will just sit around instead of creating value. This is mainstream, at least if you consider Krugman mainstream.

The thing you refer to as mainstream seems like nothing but Austrian morality play ("we've spent more than we have - now we must face the painful but healthy catharsis").

Peak oil is not an energy crisis. It is a liquid fuel crisis.