We're getting pretty long here so let me touch on jsut one or two points

Bad phrasing on my part, the intent of the comment is to say that if the number of people in the accumulation phase outnumber those in the distribution phase it is possible to have more in than out, obviously this isn't true if the distribution phase pays out more per average person per unit time then the accumulation phase takes in per average person per unit of time except to the degree supported by profit from savings/investment in excess of inflation. If we were talking about glass beads everyone put into the communal heap at a rate of one per day for X number of years and withdrew for Y number of years at the same rate the comment functions. More properly "Any system which maintains an equal or higher rate of accumulation than distribution which relies on perpetual growth is non-sustainable, and hardly requires applause when it achieves a surplus via a parallel to a Pyramid Scheme."

Or "A group that traditionally has been very worried about population growth seems bizarre to tie the sustainability of its entitlement system to said growth continuing forever and consistently."

I didn't say I think we should default or that it would even be moral, but that is the reasoning used by many a bankrupt nation or even old family when justifying welching on debts and its hardly utterly absent of logic. Nations can avoid this problem entirely by simply not deficit spending without extreme need.