How do you distinguish between censorship and social consequences inflicted by other free people?
Social consequences inflicted by other free people are those things which free people (i.e., those who are not incarcerated) enact upon you within their rights. These most exist in the negative: This is the right to not shop at your establishment; the right to not hire you to work for them; the right for them to not be near you, engage with you, or otherwise pay attention to you.
A simple way to think about it is that people whose opinions are far from the mainstream have to put in the intellectual work to convince people to associate with them if they value that opinions expression more than their own cohesion inside society. This is fair, as it's been demonstrated effective for various groups.
By misconstruing free speech to mean that the government ought to force private institutions to give everyone a microphone skews this work. It amounts to the government forcing private individuals to sponsor things they disagree with, and removes the ability of free people to disassociate themselves from that speech.
If it is not objectionable because enough people agree on it, does that significantly blur the line between censorship and social consequences?
No, I don't think it's objectionable, since the institutions that people are forced to sponsor are public, and subject to the public's review. If people were forced to sponsor a private organization, I would find that objectionable, since those institutions are not subject to public review. That is better left to shareholders.
You might not be imprisoned, but you can be made homeless, unemployed, unsafe, and alone. I'm not convinced that kicking out the bottom of Maslow's hierarchy is any better than imprisonment at the end of the day.
But this has always been true; it's now just easier to be put in that state if you misread the Overton Window [0], or the Overton Window shifts faster than you can delete your posts.
Prior to social media and the massively amplified speech platforms, the consequences of out-of-window speech were limited by how big your megaphone was, and the social consequences of associating with a person with outsider views was limited by the extent that people even knew who you associated with.
In the era of hyperconnection / hyper visibility, the risk to the individual is greater in both negative effects of associating with an outsider and in being that outsider. Can you blame a company or person for not wanting to associate with someone who risks having the Eye of Sauron shift to them? If the mob came looking for the guy in the red shirt, wouldn't you look down at your own to make sure its shade was safe?
The only solution, in my view, is to not put yourself in that position to begin with. Either post without your real name (and maintain the publicly acceptable persona) or disengage entirely. All the more reason to protect anonymous platforms, ones that are libre/distributed, etc.
Then having laws prohibiting slander, libel, fraud, harassment and incitement to violence also means we don't have free speech, since that is the state saying "people who say the wrong things get what they deserve."
I think all but the most hard-core an anarchist free speech advocates would agree with those limits to speech. Even Benjamin Franklin had limits to what he was willing to publish, as recounted in a comment here[0].
Freedom of speech does not mean all platforms must be forced to host your speech, nor that all people must be forced to consider it. The line between social consequence and censorship only tends to be drawn between agreement and disagreement with the speech being rejected - it's social consequence when you agree with it, and censorship when you don't.
If that means we don't have free speech, then I guess we don't have free speech and, more to the point, have never had free speech.
For what it's worth, I agree with you about not forcing platforms to host speech and with your point about the line being drawn arbitrarily. I think that free speech can be both a legal right and a value that is shared by the members of a society.
Edit: The Ben Franklin quote shows that he wouldn't publish anything he thought unworthy, but he would still print it for people, so he didn't refuse to do business with the people whose writing he found abhorrent.
The answer to such a question is always "somewhere".
In the case of censorship, I would argue that the line should be drawn to encompass much more than just government sponsored censorship (and even exclude some government sponsored censorship).
In the case of discrimination, I would agree that the line should be drawn before discriminating against unqualified canditates.