Twenty years ago, a young investor named Bill Ackman made an astute observation about indexation to investing legend Charlie Munger. “We’ve heard a lot of discussion about how institutions and individuals use index funds,” Ackman, then 30, said to Munger at The Buffett Essays Symposium, a conference that took place in October 1996. “But to the extent that more and more capital becomes indexed — and if you think about index fund managers as really being a computer, then in terms of the voting of shares for instance — the more stock that is held by people who don’t care about individual...