It depends on what the legitimate purpose of the market is. Is it a forum for printing money, or a forum for people investing money and taking measure risks? Right now, high speed trades are effectively using physics to cheat the system, executing trades at a rate several orders of magnitude greater than anything a human could possibly be actively involved with. This isn't the same as algorithm based trading where you make stock picks based on a stock's performance and set limits on how much risk you're willing to take.
High speed trading involves exceptionally accurate monitoring of conditions across the entire stock market, making automated calculations of network latency and fractional pricing differences to chisel off fractions of a penny per trade, but repeating the behavior on a large scale to take in billions of free money with minimal risk to the company and no measurable benefit. Before coinage had standard sizes and theft protection features, unscrupulous people would scrape off fractions of the edge of a coin and return it to circulation. Those people were called chislers. This is the same thing, just using modern techniques.
It's parasitic behavior and increasingly dangerous to the health of the economy as the automated systems amplify market swings at increasing rates.
#44 this would explain how good stocks nose dive then go back up on no news. The stock market prices are being manipulated.