It's not about front-running investments _in_ passive index funds, it's about front-running investments _by_ passive index funds, which, of course, ultimately comes out of the investors' wallets.
As a practical matter, since dealing in mutual funds' shares is settled after market, "front running" these transactions would be problematic. (Impossible, I'd say?)
As a practical matter, since dealing in mutual funds' shares is settled after market, "front running" these transactions would be problematic. (Impossible, I'd say?)