Didn't the US do something similar in 2008? They step in and take care of the banks.
The US government very much did not do that. The US let a lot of banks fail and housing prices to collapse. They did save a few banks, and most bank customers. But, most of this was adding short term liquidity to the market and otherwise healthy organizations.
PS: “Mark to market” https://en.m.wikipedia.org/wiki/Mark-to-market_accounting is an important safeguard. But, it increases the short term risks of systemic collapse.
That being said, there's a widespread belief called "Greenspan put" or "Fed put": https://www.daytrading.com/fed-put
As long as they have a semi-accurate pulse on real asset values, as a lender of last resort they have the sole ability to buy assets at distressed values. Nobody else has the ability to take a bath as the market implodes and simply create new capital to buy things at less-than-face-value.
You'd only expect things to go really bad if the Fed mispredicted actual values.