Over at the ProMarket blog, there's a great interview of Sam Peltzman on industry concentration. The whole thing is worth reading, but I thought I'd reproduce what I think are probably the most controversial of Peltzman's responses.
Q: Which industries should we be concerned with when we look at questions of concentration?
The traditional answer, embedded in the merger guidelines, is “be concerned if concentration increases in an already concentrated industry.” The evidentiary basis for this is thin. A much older literature struggled vainly for years to find a broad pattern whereby adverse effects of concentration could be localized to highly concentrated industries. I am unaware that the state of knowledge on where we should be concerned—or indeed if we should be concerned—has improved much. Basically, antitrust policy relies more heavily on beliefs rather than a strong consensus about facts.
Q: The five largest internet and tech companies—Apple, Google, Amazon, Facebook, and Microsoft—have outstanding market share in their markets. Are current antitrust policies and theories able to deal with the potential problems that arise from the dominant positions of these companies and the vast data they collect on users?
See my answer to [the question above]. It is hubris to believe that economists and antitrust officials can predict the future, which is what you need to do in this sector. Who remembers that free web browsers were once thought to be a dangerous threat to competition?
Q: President Trump has signaled before and after the election that he may block mergers and go after certain dominant companies. What kind of antitrust policies should we expect from him? Pro-business, pro-competition, or political antitrust?
See [the questions above]. I prefer humility to hubris.