Recently Cambodia has passed a law which outlaws the denial of crimes committed by the Khmer Rouge. People can receive up to two years of imprisonment. Many Western countries has passed similar laws for denial of the holocaust. Classical liberals are against any of such laws, because they are a violation of the right to free speech.
Some people will argue that crimes against humanity are facts not opinions and therefore they are not covered by the freedom of speech. Classical liberals reject this argument. After all who is to determine what constitutes a fact and what an opinion? Often there is no clear-cut distinction between facts and opinion. For instance, when scientists are discussing different hypotheses. Are these opinions? When a hypothesis has been confirmed by evidence, it’s considered a fact. Science is about establishing facts regarding the world we live in. However, science is also about questioning the things we consider to be facts.
A more important question, is why we should give facts any legal protection? As far as I am aware of, there no laws in any country outlawing the denial of gravity. Any such bill would be dismissed as ridiculous. Generally, it is accepted that facts should speak for themselves.
According to classical liberalism the litmus test for determining whether an action should be prohibited (or regulated) is the harm principle. Only if an action results, or might result, in (physical) harm to third parties then the government is entitled to prohibit said action. Therefore the question becomes: Does the denial of historical facts constitute harm? Although people might be offended by such denial, for understandable reasons, no one is actually harmed by such denial.
John Stuart Mill, the philosopher who has formulated the harm principle in his On Liberty, has also given the most profound defense of practically unlimited freedom of speech. He presents several reasons for allowing broad freedom of speech: An opinion which some seek to suppress, might be true; further by being forced to refute obviously false opinions we are able to know why certain facts are indeed true.
But Mill made a few exceptions to the freedom of speech. In his famous example of a rioting crowd, he argued we should not give a speech to such crowd which might incite them to commit violence, even if such speech could be published in a news paper. Thus, incitement to violence is not covered by freedom of speech.
Further, Mill has also argued that though the government is not permitted to prohibit the denial of historical facts, people might censure the fellow citizens for their opinions. We are not obliged to provide people the means to promote their views, nor are we obliged to associate with such persons.
Our conclusion is that governments should not be in the business of outlawing denialism.