As far as I know, market makers still have this obligation.
I believe Taleb has argued that HFT liquidity disappears when it is most needed, like seat-belts which work all the time, except during accidents (his metaphor may have been different)
Paul Wilmott argued that this much liquidity is actually not necessary. If someone will have trouble getting out of a stock, maybe they will think twice about getting into it.
Of course, an HFT practitioner doesn't need to prove to anyone why their activity is beneficial to society. The burden of proof is on the critics to show why this activity is harmful.
I believe Taleb has argued that HFT liquidity disappears when it is most needed, like seat-belts which work all the time, except during accidents (his metaphor may have been different)
Paul Wilmott argued that this much liquidity is actually not necessary. If someone will have trouble getting out of a stock, maybe they will think twice about getting into it.
Of course, an HFT practitioner doesn't need to prove to anyone why their activity is beneficial to society. The burden of proof is on the critics to show why this activity is harmful.