In Some Elementary Comments on The Rights of Freedom of Expression (here or here) (1980), Noam Chomsky writes
it is precisely in the case of horrendous ideas that the right of free expression must be most vigorously defended; it is easy enough to defend free expression for those who require no such defence.
It is a sad thing that the idea of Freedom of Expression, for which thousands have suffered and died, has slowly been abandoned in many countries of the former Free World. Today, people are prosecuted, fined and imprisoned for no other reason than uttering opinions that have become illegal. Here is a British historian, handcuffed, facing some judge in one of the several countries which find that he has no right to speak out.
If you think Perhaps he deserved it, let's first see what he said, you are on the wrong track. Return to the quotation above and read it again.
By the way, if things had to be true to be freely expressible, the world would suddenly become very quiet. With creationists, freaks of flat/hollow earth and fake moon landings, politicians would be the first to turn mute.