This article is at best inconsistent, at worst self-serving.

Funny that Cuban wasn't complaining about traders when they were driving up tech stocks in the dot-com bubble that eventually helped him land his giant payout in Yahoo stock. Or the traders that took said Yahoo stock off of him when he wanted to divest himself (aka liquidity).

Tax breaks for long-term investors? Well VC and PE firms are "long-term investors" and they already have a pretty sweet deal on carried interest. That didn't stop them from rampant speculation in the tech bubble, or buying companies at outrageous debt multiples in the credit bubble. Imagine how much more it would have gone on if they didn't have to factor tax into their return calculations? I bet Mark would love to get all his future speculative VC investment payouts tax free. I don't know of a major tax regime that doesn't treat short-term trading revenue as income as opposed to capital gains. Tax breaks for "real long-term investment"? Yes, it's called a 401k or pension plan. If you're really a long-term investor a 10% algo glitch (4% actual down day) shouldn't even register for you. You shouldn't even be looking at the market on more than an annual basis.

"The market has changed over the last 3 years" and is driven by macro issues? Yes we've been through a severe global recession driven by the bursting of a global credit bubble. Of course macro issues have dominated and volatility has been extremely high.

(The wider) Wall Street's business is not and never was purely raising capital for companies. In the 20s were market volumes way less than capital raised as a proportion? I doubt it, but even if so it sure didn't prevent the Great Crash. Why does government need to further incentivise capital raising, that already brings in some of the highest possible fees (on individual transactions) to investment banks of any "traditional" activity (equity and debt underwriting, M&A, market making), i.e. excluding principal business and super exotic trades. He also says that companies never go public anymore, yet global IPO volumes are the highest in a decade (http://www.efinancialnews.com/story/2010-03-26/global-ipo-q1).

The only point I really agree with is leverage - it fuels the growth of bubbles, and exacerbates their bursting (or causes it when taken away in some cases). Most of the major bubbles/crashes in the past 100 years were either caused by excessive leverage (credit bubble, LTCM, various debt and currency crises) or had leverage as a major feature in their bursting and the speed and volatility of the movements (dot-com, Great Crash, credit bubble). The possible exception to this is '87 (to a large extent computer-driven, arguably) although again leverage played a big role.

Finally, the major, unforeseen crashes have typically come about due to opaque, illiquid and/or highly leveraged situations (AIG, LTCM, CDS on CDOs, day traders buying tech stocks on margin etc). High-frequency traders only trade in the most liquid instruments, so ironically they are the ones trading on exchange, transparently and with exchange-set collateral and trading rules. Certainly illegal activities such as real front-running should be stamped out. Possibly things like flash orders too. A level playing field should be ensured. But he should worry more about the stuff going on off exchange than in the public markets.