What you call "fantasy" is precisely why antitrust laws exist.in the fantasy world where there are "good" and "evil" corporations and if you can just eliminate those darn evil ones everything is ok...
If all corporations were equally evil, then no single one should be allowed to reach market dominance. But no, it is only monopoly abuse which runs afoul of antitrust and leads to government intervention. And the remedy is ensuring that the company does not have the ability to repeat such behavior, e.g. through breaking it up in several parts.