The fact that there is no nuanced consideration to sell is why i...

The fact that there is no nuanced consideration to sell is why i started looking into it and i believe that it can work in the other direction to the way you believe it to.  In a massive liquidation event, i personally believe that discretionary traders would be some of the biggest emotional 'sell at any price' culprits whereas the machines will just sell when they would have usually.  Sure, considering they make up 75-80% of the market then yes you would think that they would make up 75-80% of the sell down but i wouldn't say that they caused it. 

take myself for example.  In february when i was still discretionary trading i got spooked and liquidated about 60% of my positions (sell at any cost) on about the 3rd day of the drop because i reached my limit and panicked.  I would have totally contributed (as much as my measly portfolio could) to the sharp selloff.  If i was running an algorithm at the time i would have only sold them when my stops were hit at the opening of the next days trade.

I just find that its easy to blame them when i personally think they dont contribute to it any more than any other factor.  We are just in a volatile topping phase within a normal bull/bear cycle.  

I really like this guys research and content https://bullmarkets.co/ and he releases a market wrap every day or two.  He is the one that has convinced me we are slowly topping out and that the bull will most likely be over q1 or q2 next year and that well just jump up and down in a very volatile manner until then.

sorry i didnt add a link to the podcast i was talking about before: http://bettersystemtrader.com/055-adam-grimes-market-behavior/

just a funny thing i just remembered regarding algos: i listened to a podcast on the way to work the other day and the subject was what 12 different professional algo traders did with their algorithms leading up to and during brexit.  half of them turned their systems off.  Now as far as im concerned, as soon as you allow discretion to tell you to turn off your system, your algo is no longer purely systematic.  Brexit was obviously different as it was a known news event but it was an interesting podcast.  i can find the link if anyone wants.