Yes, if zero stocks are bought or sold that's a problem. Note you don't need as much active investment as most articles claim - percentage ownership has nothing to do with it. It's the volume that changes hands.
If a dozen active investors are buying and selling 1 share of AAPL every minute, reflecting updated estimates of price... you have a market, even though it's 1 share trading out of billions. When 99.9% of investors hold, the activity of the last 0.1% of shares determines the market.
I also think 0% turnover doesn't reflect even buy-and-hold investors actual behavior. Selling 3% of shares once a year to re-balance is 3% bought and sold. People accumulating in their retirement accounts buy throughout the year. People in retirement need to pay expenses, and can sell a portion to meet them. Each of these buy and hold investors is actually buying and selling.
So between the small number of shares actually needed for a market, and the behavior of actual passive investors, I don't think the scare tactics concerning 100% passive investing are accurate.