I don't think he's implying that literally everybody trades passively, of course Zuckerberg is going to actively trade his Facebook shares, I'm going to actively trade my stock options at Public Company X, the guy down the street will still rent his house out instead of selling it and investing passively.

Plus, it's not like passive investing causes securities to never be traded, when I buy into a mutual fund I'm buying stock from someone. That someone is probably retiring and selling their securities.

Lastly, most "active traders" just buy a bunch of Blackrock/Vanguard/SPDR index funds anyway and call it a diversified portfolio that only they could deliver.

There would be a price without the constant underlying activity as well. This is basic financial economies.