During market draw downs it's the short sellers that are buying first. Without short sellers bubbles would get bigger because no sellers taming them and their bursting would be much harsher as you would only have sellers. Shorting also allows one to invest in a company while shorting others in the sector in order to invest in a company while hedging broader economic risk. Also buying put options allows you to insure your own risk. These are sold by market makers that are able to hedge their own position by short selling, without short selling no more insurance.
> bursting would be much harsher as you would only have sellers
I'm not sold on how much of a cushion that is. Shorters want it to fall as much as possible, in an ideal world all the way to zero so they don't effectively owe anything. There's no reason for them to buy until they think it's hit bottom and they also have incentives to drive the price lower with bad press and any other manipulations they can think of.
