High Frequency Trading is basically ELECTRONIC FRONT RUNNING.

Front running is the illegal practice of a stockbroker executing orders on a
security for its own account while taking advantage of advance knowledge
of pending orders from its customers. When orders previously submitted
by its customers will predictably affect the price of the security,
purchasing first for its own account gives the broker an unfair
advantage, since it can expect to close out its position at a profit
based on the new price level.
HFT firms use their extreme speed and extremely close proximity to the exchange's matching engine to be the first to see the bid submitted to buy 10000 shares of ABC. The HFT firm then uses its speed to buy all the lowest price shares of ABC and immediately offers
to sell them at slightly higher prices. The ABC investor is too slow to
know what is happening and pays the higher prices unaware his trade was
FRONT RUN!
The argument that HFT firms provide liquidity is coming
from exchanges who stand to benefit due to TWO trades taking place
everytime a large investor wants make one trade. Technology can be
used for good and evil - this is a great example of that. Why would an actual investor buy microwave towers??
http://www.businessweek.com/articles/2014-07-24/high-frequency-traders-…