There's been a lot of interest lately in the hypothesis that increased passive investing might cause non-competition as mutual funds hold shares in every company in a sector. It's now gotten a couple studies from both academia and even the Federal Reserve, and so far the evidence is that there is nothing to worry about yet. Check out Matt Levine's daily column and the "Should index funds be illegal?" section, he's been following these developments.

That doesn't necessarily mean it won't be a problem in the future. Right now the big index funds like Vanguard and BlackRock own something like 10% of public shares. If they reach, say, 50%, we might have to revisit this, but for now, it seems to be a non-issue.