"*something* has to cover that collapse in the private share of GDP" - here in Britain, we have another idea:
http://www.thesun.co.uk/sol/homepage/news/3175128/Virtual-reality-high-street.html
and yes, I agree with your approach - public spending is a compensation for the failure of private accumulation. But to me that says that it is itself a bad thing, not a good thing, that society relies on the state to prop it up. The case for the abolition of capitalism, certainly, but that would also imply the abolition of the state.