What do you mean you can't halt a bank collapse? That's exactly what we did. There was a solvency issue when panic ensued after MBS's blew up and we were able to limit a domino effect of bank failures after moving fast to inject capital into the system.

Do you mean it in a philosophical sense similar to the idea that every company will eventually go bankrupt given enough time? Any major crisis is capable of bringing down banks, its inherently a feature of fractional reserve banking but the benefits have so far outweighed the risks.