I think you have it the other way around: liquidity providers as a group make less money because of HFT, not more. Ordinary investors now pay less for liquidit

I think you have it the other way around: liquidity providers as a group make less money because of HFT, not more. Ordinary investors now pay less for liquidity than they used to because of HFT and the complaints are largely coming from traditional liquidity providers who were able to extract more for providing liquidity in the absence of competition from HFT. It is a zero-sum game but I think you're ignoring the presence of other rent-seeking players that HFT has now outcompeted. Now things are a bit more complicated because HFT is a fairly broad term but this is true in a broad sense.