No, there's about 30,000 "day traders" in the US (statistics from EBSCO host) that is an old figure though maybe they've doubled in number or such - most I meet are generally teenagers 18 to early 20s...
I don't think the massive volume changes are made by traders but rather - by intermediates. People who see a better position and want it so they sell off something else of theirs (I do that...) or by large institutions who are looking to sell off millions of shares or buy millions of shares at a time.
I think traders are viral though because for what little volume impact they may or may not have they do have a potential to drive or lead speculation and panic just like anyone else only traders and intermediates closer to traders (say someone who buys and sells over weeks not days) generally don't know a flying fuck about what is going on.
Just my biased opinion on that one but I base it on my continued success and their continued failures...
Since the Fed generally helps fundamentals its generally a boon to investors over traders
