The real fear is not domestic bank failures; but rather, that the influx of foreign capital will slow or stop if the government does not buy up the bad debt. If foreign capital is spent elsewhere the American economy will simply not have adequate revenue to maintain itself.
Wall Street banks know very well that the bailout is needed to protect the integrity of the United States as a recipient of foreign capital. It is desperate to alleviate the losses to foreign capital suppliers. Otherwise they will simply invest in other regions. The American economy is largely dependent on bringing in outside revenue. If the United States financial system cannot protect the foreign suppliers it is destined to crash.
The federal bailout is viewed as absolutely essential to reassuring the international capital markets that the United States is still a safe credit risk. If the American financial community cannot protect its international money flow from bad debt that flow will evaporate and take with it the financial system that has been built up over the past two decades.
For obvious reasons this is an impossible sale to the American public which would never willingly accept bailing out the Saudis or the government of Singapore. However; this is exactly what the bailout is required to do and why it is absolutely necessary. For Wall Street this ulterior need must be kept well hidden or it will never fly. Oops. I think I just spilled the beans.