The big investors don't have control over the leverage cycle; the banks do. What kills a leveraged bubble is when banks won't lend any more for leveraged investments. Then leverage quits making the market go up. Then people realize that the market isn't going up constantly any more, and so a few get out. Then the market goes down a bit, and some people who are leveraged panic and get out. So the market goes down more, and a lot more people who are leveraged panic...

The big investors can do whatever they want. They don't have the final control here.