Any monopoly needs to be checked. Not just corporate monopolies. It is perhaps a law of human nature that a monopoly is eventually going to start overreaching.
Previously, as a society, we break apart various monopolies. Such as Rockefeller's oil business (Standard Oil was eventually broken up in 1911, background here), AT&T, etc.
Today when we think about monopolies, Microsoft definitely comes to mind. Google has been coming up (especially in Europe). Facebook now.
Beyond this though, consider:
Government is no different.
Public schools should be no different.
However noble the business is. However noble whatever it is the people are doing.
A monopoly is a monopoly.
Left unchecked and allowed to grow too big, they eventually are able to impose their will.
The court system. That is another monopoly.
Any business and government you want to start with the presumption that they start out with the best of intentions and that even in monopolistic behavior they are still (at least for themselves) operating with good intentions.
However, it is the passing of time, the consolidation of more and more power, increased inward thinking, or however we want to psychoanalyze what happens within a monopoly. Whatever it is, the monopoly entity ends up negatively impacting those outside the entity. And the monopoly ends up increasing its own, power, wealth and corruption.
As a society, we must always do better. All of these monopolies (government and private) need to be objectively reviewed. And big changes should be welcomed.