Well, let's look at the fundamental motiviation of HFT: making money.
OK, nothing wrong with that. However, we, as a society, have reason to question how everyone makes their money. Lots of people don't want a minority of people to make money clubbing baby seals. The value generated by that practice (nice fur) is not high enough overall benefit to society to justify it.
What is the net result of HFT? The people doing the HFT make money, sure, but what value are they generating? Nothing, as far as I can tell.
HFT constitutes a tax on everyone else in the market who is going to hold onto a position for more than a couple seconds. Anyone who is a long-term investor. Every sale you make, will generate less profit. Everything you buy will be more expensive. HFT is just siphoning off money from everyone else.
The markets work because they allow more efficient allocation of capital to useful functions, and they move money away from non-useful (or at least not money-making) functions in society. This is good. HFT is sand in the gears. And don't give me arguments about how they provide market liquidity, the markets were doing just fine before this practice started.