Proprietary trading was justified not because it created large profits for banks (it did), but because it was supposed to create markets and provide liquidity for rarely traded instruments. The banks themselves established what in effect were their own substitute markets, which allowed their customers and themselves to price instruments that would otherwise have been impossible to value.
今日讨论的焦点主要不是银行给客户造成的危险，而是给纳税人造成的风险。为自营交易辩护者，不说它能给银行带来巨额利润（这一块利润的确丰厚），而是说它有做市功能，能够为那些罕有人交易的金融工具提供流动性。据说，银行建立起来的市场实际上是它们的内测市场，主要功能是方便银行及其客户对某些金融工具进行定价 —— 没有市场交易，这种定价通常是不可能的。而由此得来的巨额利润则被说成是提供一种公共服务所应得回报。