The problem is that this guy sees what Wall Street does and thinks when Bitcoinica does it it must also be evil.
What Bitcoinica does is not what Wall street does. The trader's positions on Bitcoinica were not backed by actual (virtual) assets— As their FAQ said: "To make things simple, there are no deliveries of Bitcoins." Bitcoinica was not a brokerage, it was not a stock market, it was not engaging in margin trading of any kind most people are familial with. Nor was it a derivative markets with contracts backed by assets or at least strong, enforceable, obligations to furnish the assets.
Bitcoinica was a
bucket shop, a kinda of gambling business that looks on its surface like a brokerage house. Bucketshops had waves of popularity after the invention of live stock tickers allowed realtime stock data in hotels and bars all over the country. They were roundly outlawed in the US (and most of the world) in the early 1900s— because of their habit of bankrupting the unwary and because of the manipulation they caused on the actual markets.
In a bucket shop participants come to place bets against multiples of the change in price in stocks or commodities, with a house take added to the spread. There are no actual commodities traded at any point, however, and the commodities don't even have to exist (at least not at the quantities traded in the bucket shops). The operator of large long lived bucket shops may engage in moderate hedging to prevent regular volatility from putting them out of business to quickly— but the essential behavior is the same: You're not actually buying or selling the underlying asset and it's possible to end up short (or long) more of the asset than is actually available on the market. The widespread mistaken belief that bitcoinica hedges 100% is now easily disproved by the lack of an enormous decline in MTGOX's volume— if that wasn't already clear enough from bitcoinica's frequent delays to pay withdraws, trading freezes, or the impossibility of hedging shorts using MTGOX.
Bucket shops are very risky— especially ones as narrow as Bitcoinica: A large bucketshop with many 'assets' for sale could potentially cover the losses should one become wildly successful. A single item bucketshop like Bitcoinica would rapidly bankrupt if there were large price motion against their favor. So when people think about the risk/reward they often get the wrong ratio because highly successful trades are likely to never be paid— because there is no delivery of underlying assets there is no guarantee of being able to cash out your profitable trades.
Worse— Bucketshop operators have inequitable visibility into their markets and a financial incentive to abuse it: A well timed but momentary increase/decrease of a few percent will wipe out the balances of people in "leveraged" short/long positions, converting their balance to the houses' balance. Between their ability to opaquely adjust the spreads and their holding of (apparently) a good hundred thousand btc of customer coins triggering these events would not be difficult.
Bucketshops also potentially have a distorting effect on the real market— to the extent that traders don't realize that its just gambling the fact that the buckshop exaggerates the supply of long or short positions is potentially a source of inefficient pricing (This is why on real markets there are rules abolishing or at least limiting uncovered shorts and regulating when short trade can take place).
I think Bitcoinica skirted the fine line of dishonesty about the nature of their business. As far as I'm aware they did not outright make any dishonest claims, but their appearance left many people with misunderstandings and they have happily sat quietly while other people told outright untruths in support of them. Fortunately(?), their failure took a form that could have befallen a real brokerage created by completely inexperienced people— risks that the even the biggest rubes could have foreseen— instead of the specialized risk associated with bucketshops.
I will continue to caution Bitcoin users from participating in bucketshops, just as I would discourage them from participating in classic ponzi schemes, negative expectation gambling, apparent money laundering operations, pool defrauding attacks, and fractional reserve banking — especially in the nascent and unstable Bitcoin economy.