The author mistakenly thinks that letting/making Google or Facebook censor their users (more than they already do) would prevent a monopoly and reduce monopoly advantage. How does giving monopolies more power reduce their power? It doesn't.
The only correct answer is a principled answer: censorship is wrong regardless of political affiliation.
Part of this, of course, needs to be an understanding that "free speech" was always intended to be speech first and foremost, i.e. political speech, scientific dialgues, etc. with a focus on defending things which are iconoclastic.
Obscenity is not the same thing at all, there's no need for confusion here, we can continue to ban people posting things that all good people believe should be illegal (i.e. the exploitation of children).
It's also totally reasonable for people to want to carve off curated spaces; this is why the law needs to be nuanced enough to differentiate between platforms, subforums, communities, publishers, bloggers, etc. rather than hoping to lump everything together with blanket statements that fail to accomplish the real goal of free speech.
Another way to view it is markets vs. mixed model, markets where they believe they work and socialism where they believe that makes sense.
Health care is an easy to see fault line.
Establishment types are perfectly happy to see rhetoric critical of them censored right along with the right.