The trouble is that that HFT is basically driving market makers out of business. Traditional market makers were obliged to continue trading even when the entire market had gone to shit, a service they could afford to provide thanks to their profits during normal market operations. The new breed of HFT firms that have displaced them don't do that, so as soon as the market goes a bit funny all the liquidity vanishes and people can't actually trade easily.
You say "traditional", I think you mean "designated" (or "specialist"). Designated market makers also received certain privileges, but in turn are obligated to maintain an orderly market.
Historically, not all market makers were designated market makers.
Some HFTs (e.g. some branches of Goldman) do act as designated market makers, receive these privileges, and are obliged to continue trading. Others do not. Same as always, just with machines replacing people.
