Monday saw the first ever limit down halts on major equity index futures (YM/ES/NQ) on CME Globex. It was an unmitigated disaster. It happened at a critical t

Monday saw the first ever limit down halts on major equity index futures (YM/ES/NQ) on CME Globex. It was an unmitigated disaster. It happened at a critical time (heading into the cash open), and caused chaos in the ETFs that have these futures as the underlying. Market makers price and hedge ETFs like SPY (the Spyder S&P 500 tracker) off the future. So being unable to do so since the underlying was frozen, they did the only thing they could naturally do and blew out their spreads and backed away. Even then, some unfortunate and panicky people crossed those spreads and some SPY changed hands at -14%. There is no legislating against stupidity. Then when ES and the other futures did unfreeze, they promptly plunged to a second limit down in extremely thin trade. Why so thin? Because when you stop trading, everyone empties out of the orderbook, and they don't necessarily dive straight back in once it unfreezes. Liquidity gradually comes back as participants assess that the price is stable and they can start quoting again. Monday was not a good day for your argument.