Why do we have stock markets?

Wired has a most interesting piece, mostly about why stock traders want to trade at as close to light speed as possible, and how that's being accomplished, but the article also raises a fundamental question, and gives a disquieting answer:

"High-frequency trading raises an existential question for capitalism, one that most traders try to avoid confronting: Why do we have stock markets? . . . Trading increasingly is an end in itself, operating at a remove from the goods-and-services-producing part of the economy and taking a growing share of GDP . . ."

I'm not an economist, but I'd suggest a small tax on each stock/commodity/futures/whatever transaction.

Definitely worth a read.