> Only the most hardcore market fundamentalists/objectivits tend to disagree about this principle, in my experience.
Even if the court agrees in principle, it still needs a adequate legal basis to issue an order. Violation of a law, or a contract, or whatever. I asked the GP, who seems to have experience with such cases, what this legal basis this could be.
The legal basis to intervene is there, but may be vague and open to interpretation.
For instance, a near-monopoly position might cause other regulations, like laws against unfair business practices to be interpreted more strictly than for other intermediaries:
https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:02...
As long as the population within a jurisdiciton univerally supports the principles behind a ruling, finding some regulation to support it usually can be done.
In the US, there seems to be two factors that make it a lot harder to enforce such regulation (to the extent that they even exist there) - The fact that these companies are American and able to buy influence through lobbying and contributions - The current division in American politics, where virtually any position supported by one side automatically will be opposed by the other, causing paralysis
Once you have monopoly or near-monopoly, you become more like infrastructure, whether you provide electricity or access to customers.
At that point, you either have to expect to be willing to host anyone who stays within the law, or have the monopoly broken up.
Only the most hardcore market fundamentalists/objectivits tend to disagree about this principle, in my experience. (Which means practically nobody outside the US). Though some seem to be quite willing to accept abuse of market power if it primarily hurts their political enemies.