The early 20th century put a lot of Monopoly and Trust Busting laws on the books that say some of this is illegal, not just "ought to be". What we've lost since

The early 20th century put a lot of Monopoly and Trust Busting laws on the books that say some of this is illegal, not just "ought to be". What we've lost since then hasn't seemed to be the laws themselves but the willpower to regulate in the spirit of those laws and executive power to enforce those laws.