Passive investors were not going to make the market more efficient anyway since they are not informative. They carry only one piece of information which is that

Passive investors were not going to make the market more efficient anyway since they are not informative. They carry only one piece of information which is that they have some money to invest into the economy and would be okay to take some risk, and they express that well enough through a passive financial product reproducing what the financial industry itself calls the "market returns." They of course do care to make some money; nobody is in it to lose money, so how are they making the market less efficient? It's not that different from saving the money in a bank for the bank to allocate. Now, if the passive investment flow comes to dominate volume on any given day, then the "marginal" trade becomes a passive, uninformative one; then we have a problem.