ousing market in 2004? Why was it actually not so ludicrous that the housing market could fail? What was the weakest link in the securitization chain?...

Why did it seem ludicrous to bet against the housing market in 2004?

Why was it actually not so ludicrous that the housing market could fail?

What was the weakest link in the securitization chain? In other words, which entities (investment banks, rating agencies, investors, mortgage companies, home buyers, credit default swap purchasers) were the most culpable in the financial crisis of 2008? Why?