I think you're right and you could reasonably claim HFT is a stupid zero-sum game, leading to flash spikes when algorithms go wrong real-fast.  The defenders might claim it adds liquidity but traders were trading before HFT and liquidity was fine, and what human needs sub-microsecond liquidity.  People should be investing not speculating by the day, minute or now microsecond!  A bit of short-term speculation helps liquidity and remove exchange differentials via arbitrage and reduce spread via volume, but there need to be sanity limits.

Adam