I remember when the Dow-Jones reached 10,000 Alan Greenspan warned the investors from bubble. It was well before the housing bubble. But the bulls like the bulls, continued their rush towards the inevitable brink. I believe Greenspan learn then a lesson, that he is not really controlling the situation and better not to try to avoid the unavoidable. Rather he prepared tools for the day when the crisis comes. Also he knew, that if the crisis comes, better if it will be not a mild one. He knew in a mild crisis no stimulus of trillions could go through the US political institutions. Even with the perspective of disaster at 2008, the first vote about the stimulus, still under Bush, ended negatively. I believe, Greenspan and like him understood very well that it will be better to have a big crisis than a small one, and then the frightened politicians will let the professionals do what is best to their understanding. Just try to imagine what would happened if the US congress would act as irresponsibly at 2008 as it is doing it in these days, opposing everything without any explainable reason. Today they do it because they can do it without to feel that they are threatening the whole system. And we all know, nothing is sacred in politics but the system.