For the most part, important functions of commerce are already safe from any reasonable attack. Backups, decentralized computing systems, and alternative methods of doing business are part of any business plan.

After all, a reasonable businessman has to take many kinds of disasters into account other than terrorism: fires, floods, hurricanes, earthquakes, power outages, deliberate attacks by disgruntled ex-employees, and many other unforeseen circumstances.

We didn't take a financial hit just because the WTC was wrecked. The actual economic functions of the WTC were rerouted effectively in a very short time.

We took an economic hit because the dot.com bubble had busted, tax revenues from the bubble vanished, we had sudden and unexpected military and domestic defense expenses that ate more taxes, and the airlines took a big hit (except for the small independents, which are doing just fine. Wonder why?)

Most importantly, we took a psychological hit, which is all the stock market needs to screw it up sometimes. Right now certain people are trying to make sure we don't recover until after the elections, which is why positive economic news is hard to find and negative news is on the front page.