HFT has clearly lowered spreads. This isn&#x27;t even in dispute.<p>The issue of market makers pulling out during a crisis is a regulatory issue; an market maker might do the right thing and push the market back towards where it should be and then be punished by a regulator who breaks the buy trade. If this behavior is undesirable then eliminate the &quot;clearly erroneous trade&quot; rules.<p>Your citation also doesn&#x27;t address any specific mechanism by which a delay would improve things. All it does is speculate that speed might be bad due to fat tails and handwaving.