I said 'sufficiently coercive', because the equivalence is in the limit. Even just one corporation that you can opt out of is a step up from government in many regards. But it can also be a step down in other regards if there are fewer ways to influence that corporation, and the consequences of opting out are significant.
There are of course differences in the ways you can "address, rebuke, curtail, and prevent that control" based on the specific details of the entity - just as there are stark differences between democracies versus dictatorships, and publicly traded corporations versus privately held. And when we're talking about pushing back, those details should certainly be mentioned.
But my point of emphasizing the similarities between the two large categories is to preempt this all too common pattern of people justifying corporate oppression by framing it in terms of voluntary association, while turning a blind eye to the actual coercive dynamic. I'm sure we do agree on a lot of things, but honestly your first comment is ripe with laying the groundwork for such type of justification. Corporations can certainly prevent you from speaking your mind - for example a geographic-monopoly Internet provider that censors based on content. The next step in the argument is of course "you can still speak your mind, just not using their infrastructure", but given that the sheer majority of speech is online today, that reasoning is specious - it's deliberately ignoring the power the company is actually wielding.
Or coming at it from the other direction - if it's definitionally impossible for corporations to exercise coercive power, then why is accumulating such power one of the tenets of business ("build a moat"), and why are so many people so damn interested in having certain corporations perform censorship?
An uncomfortable truth is that the main thing preventing corporations from having their own full-blown armies is the bona fide government. This circular dynamic is why I've come around to viewing freedom as a kind of logical reduction yin-yang rather as a unidirectional gradient - if the bona fide government disappeared tomorrow, the net effect would actually be the loss of much freedom, as those other aggressors would no longer be kept in check. Big-L Libertarianism sidesteps this by just asserting that having a singular military is one of the few necessary functions of government, but it's not clear why such an exception should only apply to one single topic when that same circular dynamic applies at other levels of abstraction.