Cerebral Density [UPDATE]

There's been some continuing confusion, so in the immortal words of  Roseanne Roseannadanna:  "Claaaaaaaaaaaaaaaaaaaas!"

Time for some review.

1) "Wall Street", the metaphor means stock brokering.
2) "Wall Street", the physical location, is a collection of streets/avenues in lower NYC constituting a financial district; more than just stock brokering goes on there, but so what?
3) stock trading, whether by two humans, two computers, or one of each, is a zero-sum, non-productive endeavor.  With the exception of buying of Public Offering shares, which are in the noise over any given time period, and are exactly 0 most days of a month.  The fact that "studies" have determined that 70% to 80% of trades are between HAL-9000 computers engaged in price arbitrage in time/space, only strengthens the argument.
4) the supply siders continue to argue only from their perspective:  I want X% interest earned on my money (that's my rate of time preference).  My in this case is the explicit lender, who generally is distinct from the saver(s) whose money is lent.  From the demand perspective, justifiable interest eventually is determined by the increase in physical production (real economic growth) by the most productive use.  This is the upper limit, as not all borrowers will/can engage in this Activity A, since to do so would flood the market with Widget Q, thus lowering its price and removing some, possibly catastrophic, amount of the return.  Ruinous competition, as the Robber Barons used to say.  Interest on home mortgages is not a productive use of capital, since the financial capital is not used to produce some Widget V over the life of the "house".  Housing is just consumption over time.  The interest paid is justified only by the demand by lenders for "some" return; otherwise they could put the money into companies engaged in Activity A.  Lenders can attempt to increase X%, but will be stopped by the maximum productivity growth endeavor.  And that's an asymptotic limit; it will never be reached, since if all borrowers undertake the endeavor, they flood the market with the Widget Q, driving down both its price and the return on the physical investment made to produce them.  The point being:  the interest rate is ultimately determined by physical engineering/science, not by quants on Wall Street, despite what they may think.

Point 4) leads to a problem manifest in the Great Recession:  since so much of the USofA's financial capital was put, not into physical investment, but fiduciary instruments, the return on that capital was tied explicitly to the rise in cash incomes of the borrowers.  There is no other source of cash to pay the interest.  When the interest payment exceeded cash income's carrying power, as was inevitable since median income was falling during BushII, the Ponzi melted.   There is no new plant or machinery bought with the fiduciary capital to make more/better Widget Q.  Those that still refuse to understand this, can spend some quality time with their favorite search engine.  This is well known among academic economists, and published.  Likely also well known among Wall Street affiliated economists, but they're not about to rat out the hand that feeds them.

[UPDATE]
To further point 3):  yes, there are Public Offering shares in some day's trade.  No, those shares are not sold, at the initial asking price, in regular trades.  They are distributed by the underwriters to the subscribers.  At that point they can, subject to any restrictions in the PO, be traded *between the initial owner and any computer or human* just like the rest of the shares on its exchange, because they are now just trading shares.