Because when something goes wrong, most people believe that somebody must be responsible for it. That is false. Because due to our imperfect understanding, actions have unintended consequences. And things can happen without anybody actually intending it. That is certainly true about financial markets.
Nobody wants a crash.
And nevertheless you can have a crash. And then you have an unreasonable boom, then people don't realize that it is unreasonable. Currently, the American economy is the sole winner in the world. I don't think that the U.S. economy is currently the only economy in the world. I think many other economies have benefited from international trade and the capitalist system.