Well, if the government will predictably use legal methods to prevent and even break up monopolies, that's indistinguishable from "monopolies being illegal" even if there is no explicit law that says that.
> Well, if the government will predictably use legal methods to prevent and even break up monopolies, that's indistinguishable from "monopolies being illegal" even if there is no explicit law that says that.
It is illegal to take certain acts that would form a monopoly (which is why the government blocks or puts terms on, e.g., some mergers) and it is illegal to use monopolies in certain ways to advance market power in other markets (one of the remedies for which may be breaking up the monopoly which was illegal leveraged.)
But simply gaining and maintaining a monopoly is not illegal, so long as you don't gain it by illegal methods or do illegal things with it.
The government certainly doesn't like monopolies, but as long as they are achieved in the prescribed ways and not abused, they are perfectly legal.