The fact is that market prices have risen faster than profits. Plain speculation plays a part but is not the decisive factor. The demand for stocks rises even faster than supply. Another important source of funds flowing into the stock market comes from capitalists around the world who view U.S. imperialism as protection from their own working class. And the higher the market rises the steeper will be the fall.
Excessive speculation is but one of the components creating the danger of a sever economic crisis.
Another is indebtedness - defaults in credit card and other forms of borrowing. The working class as a whole is losing economic ground and will ultimately lead to falling retail sales, major down sizing and mass layoffs - all classical ingredients of crisis. Elements creating instability, including speculation, are very strong and cannot be ignored in assessing prospects. In the long run, only socialism can solve the problems of imperialism's inevitable economic crisis.