I'm not sure if your comments were directed to me.
The October '87 drop, the post-9/11 drop, and the current situation are all very different matters.
The October '87 gave me very little concern. Overvaluation and interest rate changes sparked a sell-off, and rather easily correctible technical problems (along with some panic selling) exacerbated the sell-off. I was very comfortable putting most of my money into the U.S. stock market shortly thereafter.
9/11 gave me slightly more concern from an investment perspective, but I was still comfortable enough with the U.S. stock market to add a substantial amount to my U.S. stock holdings as soon as the markets reopened.
This latest drop in stock prices also gives me little concern. I do, however, have serious concerns with the federal government's fiscal and monetary practices. Those concerns have not abated in recent weeks.