You say that, but I don't see where Bernie is proposing some sort of blank slate.
He says he'll raise taxes on corporations and go after money stashed abroad - so that means we'll still have corporations.
He says he'll raise taxes on the top 1% - so that means we'll still have people working at those corporations, presumably at relatively high salaries.
He says he'll raise taxes on what he calls Wall St speculation - so that means we'll still have investment bankers making large financial transactions.
He says he'll raise the capital gains tax - so that means we'll still have relatively high wealth individuals holding capital (it's not just going to be confiscated).
What I'm seeing is a guy proposing to raise tax revenue through the existing economy/society to pay for HC, education, jobs, etc, but smart people analysing his plans are saying that his cash inflows are nowhere near able to cover the costs of his ideas. I don't see a guy saying "we're going to tear it all down and start from scratch!" If that's the plan, then why is he selling solutions to fit within the current model?