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This is a timely post, Mark! It's an interesting dilemma... For public companies, they have a fiscal responsibility to create shareholder value. At the core, social platforms are private companies with business goals and established guidelines. When users violate guidelines explicitly set in Terms & Conditions and Agreements (which the user AGREES to upon sign-up) give the company every right to remove the user!
However, as we've all seen, the lines between social platforms as a private entity V.S. platforms enabling the exchange of ideas on a global scale - traditionally a role perceived as "public service" is blurring. And that's why critics (as shown in your article) perceive the removal of a user (aka "censorship") violates their fundamental rights. Should social platforms be regulated as a "public good" then? We are venturing into unchartered water!