As in most things of this nature, I think a good deal is to be learned by who are the most vocal
informed opponents. The most vocal market participants against HFT are usually large, institutional market makers who used to grow fat on $1/16 spreads and liquidity rebates (Themis, I'm looking in your direction). These guys used to not have to work particularly hard for the cash, but they're getting their lunches eaten by new market participants who can do it faster and cheaper and have built their companies around integrating new tech very rapidly.
You'll find people trotting out the same old chestnuts (brain drain, unfairness of server colocation, etc.) but those are distractions from the interesting issues.
As an aside, I once had the distinct pleasure of watching a conversation on one of the CNBC programs running in our kitchen in which a NYSE floor trader actually used the phrase "we're the institutional investor looking out for the little guy" while managing to keep a straight face. This dude probably would have curb stomped his own grandmother to pick up a $100 bill. Even the usually sympathetic hosts just laughed outright.
I'm surprised that the outrage against HFT is so strong given how comparatively little is at stake there. After the HFT's much, much, much larger financial cousins, the "big bank" market participants nearly destroyed the entire planet's financial system, it's quite a coup for them that they've shifted the outrage to the guys competing over less money than some banks pay out in bonuses.
I have no love for anyone in the financial industry (I'm a self-loather, if you haven't noticed), but the HFT guys are way, way further down on my list of people to be pissed off at.