In connection with the jailing of Australian Holocaust-denier Fredrik Toben, two lawyers argue in today's Australian that Holocaust-denial should be punishable by law. This isn't a view I agree with, but I draw your attention to the terms in which their argument is made. Formally it appears to conform to the classic principle defended by J.S. Mill. Steven Lewis and Peter Wertheim say:
Like all freedoms, the proper limits of free speech are exceeded when it is about causing harm.
However, by extending the meaning of harm to cover the propagation of ideas, the dissemination of words, they loosen the principle so that it becomes next to impossible to apply in an objective way, despite their own plea to the contrary. Violence against persons, and therefore against groups of people, is obviously a harm; and direct incitement to violence in situations where this clearly helps to bring on its occurrence may be included in the same category as being a proximate cause. But the further back you go from the criminal act of violence, the more difficult it becomes to establish a clear connection between someone's speech-act in spreading a belief or idea and the violent harm itself. To criminalize putatively harmful beliefs opens the way to such notions as the defamation of religion.