Of course enforcement is imperfect, but is a price change due to insider trades really more informative than an earnings announcement heard by just-about-everyone and just-about-the-same-time?
Further, there have been a number of articles here describing exactly how High-frequency trading gains an information edge - among other strategies, by "tasting" orders, the machines can discover demand without making investments and then front-run the demand.
Insider trading has to do with with knowledge of important and undisclosed facts about a company. Stuff that, when disclosed, might cause price swings (several percentage points).
HFT works with disclosed information: prices and order books are public. Just because someone has access to this information 10 milliseconds earlier doesn't make it "insider" info. Also, HFT profit margin is usually tiny (measured in basis points).
You're stretching the definition of "insider trading" so much that it's almost meaningless.