When this country was founded Government was by far the most powerful agency in people's lives. Merchants where important, had a lot of influence but still could not be too aggressive with a regent.
Today the Government has far less influence over your daily life than large corporations and you employer. In 1776 most people where farmers, the only agency that could deny your livelihood was the government (they ultimately had control over your land). Today government policies have far less of an impact than your employer on your livelihood.
The fact that a handful of oligarchs can decided that Trump doesn't need a voice is not democratic solution to a politician I radically disagree with that I would like. If you feel like the list of things you can't say publicly without ruining your career is shrinking, that is certainly a threat to the spirit of free speech.
The solution entails more than questioning the philosophical idea of "Free Speech", it involves considering the nature of government and human rights in an entirely different light than the currently dominant neoliberal economic consensus.
So arguing that the façade of a private company being allowed to shut you down is somehow rational is nothing beyond absurd. If you cannot express your speech anywhere because a mob disapproves, you don't have freedom of speech. Freedom of Speech is not "Freedom to only listen to the things I want to hear." Otherwise there is no free speech, just what is culturally acceptable.
> the façade of a private company being allowed to shut you down is somehow rational is nothing beyond absurd
Indeed, it is, but that's where we are.
> a mob disapproves
In this case, it's not a mob. It's a handful of people who care more about making money than upholding rights.
> there is no free speech, just what is culturally acceptable.
"Yet if all cannot be of one mind—as who looks they should be?—this doubtless is more wholesome, more prudent, and more Christian, that many be tolerated, rather than all compelled. I mean not tolerated popery, and open superstition, which, as it extirpates all religions and civil supremacies, so itself should be extirpate" - John Milton, "Areopagitica: A Speech for the Liberty of Unlicensed Printing to the Parliament of England", 1644 https://www.gutenberg.org/files/608/608-h/608-h.htm
Free speech has always been constrained by what is culturally acceptable.