These advocates typically recommend stronger antitrust enforcement that would stop mergers involving large firms. Some would go even further and recommend breaking up large companies just because they are big, with some desiring to return America to the small-business ideal advocated by the late U.S. Supreme Court justice Louis Brandeis.2
The main evidence for their case is the “smoking gun” of higher profits, which they argue is evidence of reduced competition and increased monopoly.
For the full report: https://itif.org/publications/2020/05/18/monopoly-myths-concentration-leading-higher-profits?mc_cid=adfe7eb9e5&mc_eid=3171ceba53