Hawker, you're right. They won't act rationally because they act under the direction of the central banks. They like bubbles like this because it enables them to manipulate monetary policy to their benefit through the printing press. The problem lies with the central banks and their shareholders.
Maybe yours are. Here banks are not. They have to meet the Basle standards but they are very free apart from that.
Why do you stuggle with the idea of irrational behaviour being a natural part of human life? Its been well documented since the Tulip bubble that markets misfire from time to time. Yet people always look for someone to blame, be it the government, the Jews, the 1% or whoever. The very idea that irrational behaviour is a normal part of life in a free market economy seems to be treated as sacrilege.
If irrational decisions are made, then the consequences of those irrational decisions should be realized. The problem is, the government isn't allowing consequences to be realized, thus allowing more and more irrational behavior.
From the perspective of the banks, it was irrational to hold so many subprime loans. They should have felt the consequences of their irrational decisions by being allowed to fail, but the government bailed (some of) them out, encouraging further irrational behavior down the road.
From the perspective of the shareholders, it was irrational to invest in banks with such irrational lending behaviors. Those that lost money on their investments deserved it (though hopefully, they protected themselves from too much loss by diversification), and those that did not lose much money because of the government bailing out the banks they invested in are encouraged to continue making irrational decisions.
From the perspective of the homeowners, it was irrational to purchase a house they could not expect to pay for if they lost their job. Those that lost their house because of it deserved it, and those that did not lose their house because the government bailed them out through various incentive and welfare programs will continue making irrational decisions.
I still stand by my statement that government encouraged too much subprime lending through their Freddie Mac/Fannie May programs, but I do agree with you that irrational decisions on the part of various banking institutions also helped "crash" the economy. It certainly wouldn't have been as bad if the government hadn't helped inflate demand with their subprime incentives though - I hope people learn from that.