Making money from pure trading revolves around information asymmetry, and ability to store goods - most of the time this is really good, because it helps to motivate people with clever ideas to put them into practice.

The problem with HFT is that practically speaking, the value of a company can't change in timeframes shorter than a couple of hours (barring exceptional circumstances like a big announcement). So a HFT firm is not actually benefiting from information asymmetry about the product of the company being traded or real-world conditions, it is benefiting from information asymmetry about the conditions at the exchange. In theory this is transferring money from subject-matter experts to experts in how exchange servers & the local fiberoptic grid works.

I'd be alone in a room of HF traders, but this isn't useful economic activity vs. subject matter experts making money.

I don't understand all the arguments about 'liquidity', I don't see why a slight price spread is a bad thing; provided that I can sell stock in an hour or so. There isn't a magic 'efficient price' determined by the gods of the market - it is whatever the buyer is willing to pay.