"[There's something very sinister about a company that takes society's greatest engineer and science minds away from important tasks for humanity and diverts them to the task of optimizing ads]
A lot of people will say what you say about HFT, but have no qualms about Google and Facebook and Twitter. Why is that?
Setting up a global communications network where I can easily share photos videos with friends and families (helping millions and millions stay in touch) isn't worthy of some great hackers?
Because Google and Facebook and Twitter provide legitimate value and services (some more valuable than others), and offer something that wasn't there before.
HFT does none of the above, unless you believe that lack of liquidity was somehow a big problem prior to them entering the market and generating 80% of the trades, and skimming off as much money as possible in the process.