Chances are you're familiar with the arguments in favor of high-frequency trading (high-frequency trading news)--that the practice adds liquidity, that it's performing a market making function, and so on. This is a well-reasoned position, obviously. But Themis Trading has some nuance to add to the discussion. It comes to the debate from the agency trading side; it has roots at Instinet.

The firm argues that 1) high-frequency trading really only adds liquidity to the top 100 stocks, the others have struggled with wider spreads and more volatility; 2) the extent to which such trading aids in price discovery has been overstated; 3) that they trade against retail order flow in some cases; 4) high-frequency firms are anything but market markers, they have no obligation to smooth volatility; and 5) the lack of studies showing no ill effects of high-frequency trading has been overblown--it would like to see more research facilitated by the proposed HFT order tag. It also sees some high-frequency trading as predatory--when it aims to game dark pools, for example. The debate will no doubt continue.  

For more:
- here's the Traders article

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