Price discrimination can completely eliminate all allocative inefficiency from monopoly. Superficially, there seems to be a lot of price discrimination. Ban on price-fixing and collusion Impedes research joint ventures, joint use of patents, etc. Antitrust cases don't generally target monopoly in the economist's sense of the term. At most, they target a few symptoms of monopoly.
Laws are vague enough that almost any firm is arguably guilty.
Market checks on collusion and predation work much better than antitrust without the negative side effects discussed above. Abolish government grants of monopoly privilege. Evidently, all that is necessary to abolish monopoly is that the government abolish its own creations.