Agreed, but if the stock market sell off was due to the mother of all margin calls a number of questions arise:

1.  Was this the result of "guidance" from Treasury, the  Fed or the SEC?  Else, how did all of these banks come to change the margin by the same amount?

2.  Why was this done and why was it done the way it was done?  Given what London Banker lays out it is hard to imagine that "no one could have foreseen" the effects this would have on global stock markets.

3.  Were there alternatives?

4.  Why has Congress not asked Paulson, Bernanke and Cox  these questions?

This seems like a massive example of a particular answer to the old ethical dilemma of the switchman who sees a run away train and can chose between victims depending on what switch action he takes.  Given the $ Trillions of lost value in retirement funds alone, these are questions that should be asked.  Perhaps by a prosecutor.

As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."