Then let’s change the law. It’s obvious over the past few years that companies can’t be trusted with freedom of association or freedom of speech. Let’s strip them of both.

If you are incorporated (and therefore benefit from government-provided protection from liability and lower tax rates) then you no longer get to choose your customers; you’re a common carrier and must provide the same service to all customers. You can only terminate a customer for non-payment (if you’re a paid service) or if the customer takes actions that directly threaten your business (eg attempts to hack your service).

Social media companies may no longer promote or suppress content; they can only provide tools to let users do so themselves (eg filter/block/subscribe/tag). Advertisers can use similar filters for ad placement.