John Stuart Mill wrote
The peculiar evil of silencing the expression of an opinion is, that it is robbing the human race; posterity as well as the existing generation; those who dissent from the opinion, still more than those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth: if wrong, they lose, what is almost as great a benefit, the clearer perception and livelier impression of truth, produced by its collision with error.To pretend that there is not a collision of values between the West and Islam is to be both stupid and purblind. I believe that our values are right, and theirs are wrong. And foremost amongst our values is freedom of speech, thought and assembly. There must be no retreat, not one step back, on this principle.