I don’t think monopolies are in-and-of-themselves entirely legal. Eg, if you have a monopoly on ads, you’re likely committing an offense. But the enforcement o

I don’t think monopolies are in-and-of-themselves entirely legal. Eg, if you have a monopoly on ads, you’re likely committing an offense. But the enforcement of that has varied substantially over time: strongest at the end of the Gilded Age, lessened over time, and likely to be strengthened in our neo-Gilded Age.