As i see it, you already provided all aspects to label HFT as such. Except one: the physical foundation of running such a business.
They provide faster and more cost efficient liquidity, thus "bringing down the spread" which will push out maybe not all but certainly the lesser privileged conventional traders. This is foremost negative for the effected traders and not per se for the public but as the pessimist that i am, i cannot help it but see it as just another way of market consolidation, of monopolization in the worst case.
The only way to seriously compete with such HFTs, is to do it as they do, which requires the same physical accesses to the markets. Previously, the access to valuable (insider) information was a privilege for slow traders and a way to get an edge. Speed and algorithms are imo just a new privilege, enabled by technology.
The simple reason why insider trading is illegal, because it puts other marketeers at a disadvantage, they have no means to compensate. The same is true for HFT. You cannot rent the rack next to the markets machines when its already occupied.
What would you reply to such a statement: HFT is just front running but from the client side.
But to be fair, i have to see convincing evidence for my pessimistic worst cases too.