As far as sciences go, economics is about as inexact as you can get. You can find all kinds of explanations for what happened in the past, and all sorts of theories about what's going to happen if we do this or if we do that. 'Proof" simply does not exist when it comes to economics.
The one thing I will say about Keynesian economics, it probably wasn't designed for situations where the debt and deficits are this large. And projected to go higher. Going deeper into debt scares the hell out of me, don't know why everyone else isn't scared too.
Keynes would definitely say to save when things are good so that you can spend when theyre bad.
But the amount of debt doesnt matter one bit when it comes to how fiscal expansion effects the economic condition in the present. That is, if it doesnt raise interest on US debt. And in the US it wouldnt, because some institutions will always buy treasuries...always (see, bank of china).
So yes, the fact that we are in this situations is regrettable. Each solution leads to a less than desirable outcome. We can let the economy fall back into a recession while maintaing a balanced budget (because right now a balanced budget would mean recession), or we can spend more money on growth and go more into debt.
And this is the discussion we should be having. Its the only honest discussion to have. Everything else is just rhetoric.
And now im waiting for them to pounce on the "a balanced budget means recession" comment....