There is no such as thing called mutual growth. For instance, when baby boomers need cash and take their profits, other fund holders will have to sufer.
Wondering: Doubtful that their withdrawals would be all at once and for their complete holdings. Don't overlook the fact that boomers, they say, will be the beneficiaries of their parents' estates, which are said to be at record levels of inheritance. If that's so, that will certainly provide cash for them. Plus, how much impact on funds would be counteracted by the "other" fund holders, if the "others" are affluent and successful enough to drive cash into the funds, and of course, how much of a factor is the success of those funds?