You are assuming that speculators go against the flow of "commercial" players in the market, and that they buy low and sell high. But it could very well be the opposite, with speculators engaging in a herd behavior that amplifies the boom-bust cycle, with a bunch of them making a killing while the music is on (and pocketing their 20% share in the upside) and losing everything (well, their investors' money) on the way down.