The metaphor of ‘the market-place of ideas’, refers to the notion that no idea should be suppressed, but instead should be free to enter the ‘market-place’, where, to continue the metaphor, it can be bought or rejected.
Whilst he did not use the expression, John Stuart Mill sought to justify the marketplace of ideas, in Chapter two of his book’ On Liberty’.  On the subject of stifling false ideas, Mill stated:
“We can never be sure that the opinion we are stifling is a false opinion; and if we were sure, stifling it would be an evil still.
First, the opinion which it is attempted to suppress by authority may possibly be true. Those who desire to suppress it, of course, deny its truth; but they are not infallible. They have no authority to decide the question for all mankind and exclude every other person from the means of judging. To refuse a hearing to an opinion because they are sure it is false is to assume that their certainty is the same thing as absolute certainty. All silencing of discussion is an assumption of infallibility. ”
Since the imposition of lockdowns across much of the world, apparently in response to Covid 19, there has been a considerable focus on purported disinformation and with it, an implied rejection of the marketplace of ideas.
In this ARTICLE about the First Amendment of the US Constitution, an academic from Durham University expressly questions the validity of the market place of ideas as a concept. In answer to her question about the future of the marketplace of ideas, she claims:
“At the very least, it means that this is a time for serious introspection concerning whether, after 230 years, it is time to rethink this cornerstone of America’s free speech paradigm.”
The basic premise of the article seems to be that certain actors have deliberately peddled falsehoods, which has led to hostility towards the main-stream media and the acceptance of ‘conspiracy theories’ regarding Covid 19. She states:
“Such theories, along with President Trump, are fuelling the public protests to lockdown orders in several US states. While marketed as grass roots efforts by concerned every-day Americans exercising their First Amendment rights, such activism is in fact being amplified, and in some cases coordinated via social media, by far-right groups that were initially formed with the assistance of Republican megadonors. While the damage flowing from such efforts may be impossible to quantify, there is no doubt that Americans are literally dying as a consequence”.
I disagree with her factual assertions above and would argue that caustic criticism of the mainstream media is a form of free speech. However, I am only concerned in this article with the philosophical issues concerning the marketplace of ideas. When questioning whether the marketplace should survive as a concept in 2021, she opines:
“Moreover, while the ultimate objective of the marketplace of ideas is to reach truth through the competition of ideas, this principle is premised on the assumption that all voices have equal access to the marketplace and that all citizens agree both that objective truth exists and that the goal is to find it, which is clearly not the case in the contemporary US, as emphasised above. Additionally, another fundamental part of America’s free speech tradition is the principle that an informed public is the essence of working democracy. Yet, the US currently has an executive branch that is actively endeavouring to misinform the public on a routine basis and a social media environment in which such misinformation is communicated to the masses with a single keystroke.”
It has never been the case that all citizens have had equal access to the marketplace. How could such equal access be achieved? This utopian criterion, if regarded as a pre-requisite to the implementation of the marketplace, would delay such implementation indefinitely. What can be achieved, is prohibiting the forceful removal of persons and ideas from the marketplace.
As for a belief in objective truth or indeed objective morality, applying Mill’s arguments as set out above, solipsists and nihilists have the right to have their arguments heard (even if the former may doubt that there is anyone listening to them). The existence and validity of objectivity as a concept, should not be immune from questioning.
With regards to agreeing that the goal is to find objective truth, this seems to be suggesting that for the marketplace to be viable, the participants must be acting in good faith. It is obvious that the human fallibility that Mill described, would apply to judgements on whether individuals are acting in good faith or bad faith, which is essentially an empirical question, leaving aside the intangibility and complexity of matters concerning the mind.
Any challenge to the marketplace of ideas, based on the concept of pernicious lies, cannot escape the problem of human fallibility to which Mill referred; the argument would become circular.
However, even if one could prove that harm was deliberately being caused, would this justify ending the marketplace of ideas? It would not for the reasons given below.
Image for arguments sake (I strongly disagree with the following), that Covid 19 was a virus with a high infection fatality rate, even among the young and healthy. Additionally, imagine that the latest vaccines that have been developed were irrefutably safe and would save a high number of lives.
Consequently, dissuading people from having the vaccine would cost lives and if done in bad faith, could be regarded as wicked.
Would this be equivalent to person A intentionally inducing person B to drink deadly poison by telling them it was water (which would amount to murder and thus the communication would not be lawful or protected)?
No, because of the following:
Person A has intentionally harmed a specific person.
The harm is immediate.
The harm was irrefutably a direct response to drinking the poison.
Person B did not make an informed choice; they were not presented with arguments as to whether the drink was safe.
There is no right or freedom that applies in the above scenario, that is equivalent to a person having the right to refuse to take a vaccine, even if this can be proven to be a decision that is objectively bad for the person’s health.
Just as an individual has the right to make poor health choices, even ones that result in death, such as excessive alcohol consumption or a diet that causes obesity and diabetes, adults with full capacity, have an unfettered right to refuse medical treatment. They have the right to refuse such treatment after considering a range of information and if they are influenced by unreliable sources, this does not negate their free choice or provide a justification for silencing the unreliable sources. This applies to groups of people and humanity as a whole.
I have been generous to the opponents of the marketplace, in my imaginary scenario about so called ‘anti vaxxers’ (this umbrella term would cover a very wide range of people and theories); I think it is likely that they believe what they are saying, even if they are wrong (I don’t know whether they are wrong, and as previously stated, the term covers a wide of theories). Furthermore, there is the potential for the debate over a vaccine to be never ending due to the emergence of new data, which does not apply to the poisoning scenario above.
Therefore, applying Mill’s argument on human fallibility, an anti-vaccine view should never be silenced by an appeal to authority. If one doubts the ability of people to choose reliable over unreliable sources, then one must inexorably doubt the current idea of democracy.
Furthermore, it is possible to safeguard against misinformation or disinformation by providing reliable information in response; it is not possible to safeguard against evil and tyranny, once you provide the power to a body or any individuals, to silence the ability of others to communicate and to decide what information and opinions the majority will have access to.
The limits to free speech should be extremely specific and circumspect, essentially it should only be limited to prevent a specific and tangible harm and the expression of an idea should never be outlawed, per se.
 First Published in 1859
 Penguin Books 1985 edition, Chapter II p77
 E.g., direct incitement to violence, threats of violence, contempt of Court, espionage, breach of confidentiality, defamation.