It’s a truism that the First Amendment only protects citizens from the government, not from other citizens. Nothing stops a private college from expelling any student who criticizes the administration, and nothing stops a private business from firing any employee who doesn’t support the boss’ preferred candidate. We apparently place our trust in the multiplicity of the market to maintain some semblance of freedom; out of thousands of competing companies, not all will ban the same political positions; if too many did so, other companies would start offering freedom of speech as a benefit and poach the more repressive companies’ employees and customers.
It’s a little concerning that we accept this argument about freedom of speech when we don’t accept it for anything else. We don’t trust the free market to necessarily preserve racial equality – that’s what anti-discrimination laws are for. We don’t trust the free market to necessarily preserve worker safety – that’s what OSHA and related regulations are for. We don’t even trust the free market to necessarily preserve fire safety – that’s why federal inspectors have to come in every so often to make sure you’re not secretly plotting to let your employees fry. Whenever we think something is important, we regulate the hell out of it, rights-of-private-companies to-set-their-own-policies be damned. But free speech? If you don’t trust the free market to sort it out, the only possible explanation is that you just don’t understand the literal text of the First Amendment.
He goes on to develop this line of thinking in relation to the recent uproar over Reddit, and as always, it's worth reading the whole thing. I'd like to think that arguments like his would eventually penetrate some thick skulls, but I'm afraid we just live in an age where the cultural pendulum has swung further in favor of hypersensitivity to offense. It'll swing back the other way on its own schedule eventually.
To be clear, I don't believe there's any kind of law that can prevent the sort of miserly attitude toward free speech that dominates discussions today (and I don't think Alexander does either, despite the impression a lazy reader might get from this excerpt). The case in favor of a more expansive conception of the spirit of free speech is essentially a moral one.