The vast majority of people, including your humble blogger, have never done any serious research on the Holocaust. In this case, our main reason to believe it happened is that, in most relatively free countries, anybody who had the opposite opinion has been free to defend it and that, obviously, it did not survive the shock of free debates. For the same reason, most of us non-physicists believe in quantum entanglement.
What will be the consequence of the legal bans on Holocaust denialism (often through so-called “hate laws”) that have spread in so-called free countries (but not in America)? And what will be the results of Facebook’s decision not to allow the discussion of this topic (“Facebook Bans Content Denying the Holocaust on Its Platforms,” Wall Street Journal, October 12, 2020)? These two sorts of ban are very different because Facebook is a private entity that, like any other, (still) has the right to decide which opinion it will allow to be expressed on its property. But, given the importance of Facebook (and Twitter) in public debates, the two sorts of restraints may well have similar consequences.
It is true that a lot of snake oil is peddled in popular opinions and on social networks. But we find ignoramuses in the intellectual establishment too. And it is not possible to protect “vulnerable” people against these dangers if only because the habit of not being confronted with contrarian ideas may make one more, not less, gullible.
The most serious reason to oppose speech bans was expressed by economist and philosopher John Stuart Mill in his book On Liberty (1859):
Complete liberty of contradicting and disproving our opinion, is the very condition which justifies us in assuming its truth for purposes of action; and on no other terms can a being with human faculties have any rational assurance of being right.
Imagine what will happen after several decades of legal and practical bans on denying the Holocaust. There will be few discussions on the topic. Its deniers will be silent, except in private, in samizdats, or in violent groups. Its defenders’ research may have become rare because less apparently useful (and not without risk: suppose the researcher finds something that does not exactly fit the official wisdom?). The historical existence of the Holocaust will have become a sort of official mythology prone to jokes—think of the political slogans in the late Soviet Union—that most people will have no reason to believe.