The role of credit-default swaps and also how an insurance company like AIG simply could not be allowed to fail, and also having billions of dollars suddenly disappearing as we saw through the Wall Street collapse, simply cannot be ignored. And a reminder that it was the collapse of Wall Street that started the downward spiral that led to the Great Depression, so the collapse of credit is of terrible importance here.
As compared to the situation prior to the Great Depression, we actually had a higher percentage of our economy tied up in credit just prior to the Great Recession, and much of many peoples' retirement money was wrapped up in this as well, and also so were paychecks in business whereas so many of them had borrowed money to meet weekly paychecks because then they could invest their profits and get more back in return by doing it that way largely because interest rates were and are so low.
So, what I cam citing is not just from Keynesian economists but also from conservative economists like Paulson and Bernanke, both Republicans btw, and both of which warned legislators of impending doom if there was no government injection of money to keep the boat afloat. It was the latter who predicted that, without this, we could actually have ended up in worse shape than during the Great Depression, and Bernanke is recognized as being one of the foremost authorities on what is called "depression economics" because that's his specialization.
One simply has to understand that our economic system very much is like a house of cards, that can typically take relatively minor hits, but heaven forbid if it's a big hit. Just take a look at how much damage the hit we did take did to both our and the world's economies for proof if one were to have a doubt about what these economists have stated.