Freakonomicsで、Posner(たぶん世界でもっとも影響の大きい裁判官/経済学者)が新著"A Failure of Capitalism"について解説している:
When banks start to hoard cash because their solvency is impaired, the money they receive from the Federal Reserve’s purchasing activity does not spread into the rest of the economy. That is why a cascade of bank bankruptcies is far more serious than a cascade of, say, airline bankruptcies.

So the rational banker will take more risk than is optimal from an economy-wide standpoint. That is the logic of profit maximization, as explained long ago by Adam Smith: the businessman cares about his costs and his revenues, but not about the costs and revenues incurred or received elsewhere in the economy. He is not an altruist. The responsibility for preventing the collapse of the banking system is the government’s, and it has been shirked, with extremely serious consequences.
銀行は信用創造によって社会に大きな外部性を及ぼすが、それを内部化するインセンティブがないため、過剰なリスクテイクが起こる。経済システム全体を崩壊させるような不確実性(tail risk)はごくまれで、個々の銀行がそれをヘッジすることは困難なので、彼らはそれを無視するバイアスをもつ。このように個別には合理的行動の集計が社会的に過剰なリスクをもたらすのは、株主利益の最大化にもとづく資本主義の限界だ。