You want to see what happens without HFT. Look at the crash in 89, when human market makers would no longer answer their phones because they did not know what was going on in the market.
Instead of the crash recovering in minutes, it took hours and had larger widespread effects.
Furthermore, exchanges have now added automatic pauses in trading during highly volatile times, to let traders figure out what is going on.
The markets are objectively more stable, more efficient, and tighter, and better for the general public now with HFTs than they were in the 80s and 90s with human market makers/brokers.
Liquidity drying up when shit hits the fan is a fundamental aspect of markets that has been around forever
I won't go as far as to say that it's a feature not a bug. But I will say that the problem is currently the least problematic that it has ever been. Because of HFT, stability returns within minutes, rather than hours/days/weeks (which is how long it used to take before various technological innovations)
When shit is hitting the fan, participants become willing to cross _very_ large spreads to trade. It can be a lucrative time for HFT market makers, as well.
