I don't have time to study this question so my answer is useless, but to play along, I'll go with 5% or so of GDP. Why? Because the two historical periods that

I don't have time to study this question so my answer is useless, but to play along, I'll go with 5% or so of GDP. Why? Because the two historical periods that exceed 5% are (1) the Great Depression and (2) the 1980+ era of financialization leading to the recent crash. (I'm getting this from the Wikipedia graph I linked to.) To turn to your other point, I certainly respect what you're saying, but once again there's this problem of reductio ad absurdum: forces leading straight to financial meltdown can hardly be representative of a proper system. What you're saying sounds dangerously close to "the system worked". Or perhaps, "the system just didn't follow its own logic consistently enough".