The entire second paragraph is about finding optimum turnover to keep the team fresh and dynamic. I think it's impossible to control organic voluntary turnover,

The entire second paragraph is about finding optimum turnover to keep the team fresh and dynamic. I think it's impossible to control organic voluntary turnover, as you don't control people's lives/desires. The alternative would be artificial turnover, moving people in and out of teams as needed to meet this goal. I think people joining and leaving is disruptive regardless of it being organic or artificial.