Corporations aren't a threat to liberty because they lack that ability to coerce people, no matter how big they are. The State's nature lies exactly in the coercive power, in the monopoly on violence, the Gewaltmonopol des Staates.
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Corporations can threaten one's liberty by capturing the government (a political party is a corporation), but that's exactly why the government is so dangerous and the FF were so preoccupied with ways of keeping it under control. The East India Company is an excellent example of this - if they weren't under the protection of the English government, they wouldn't have been a threat to anyone's liberty. By itself, the Eeast India Company would never be able to impose a monopoly - that's why they needed the government to promulgate the Tea Act. If a monopoly isn't impose but results from the voluntary decisions (say, if a company would decide to sell unlimited internet access for a $1 per decade fee) it doesn't interfere with anyone's liberty - it would run with the other ISP out of business but there's no such thing as the "liberty to have a sustainable business".