The Australian press is in an uproar over DVDs of sermons by Sydney Muslim leader Sheik Feiz Mohammed in which he refers to Jews as pigs and argues that young Muslims should be taught the virtues of jihad. The police are investigating, and there is some chance Mohammed will become the first victim of Australia's new sedition laws. This would be both a gross affront to freedom of speech, and a terrible mistake.
There is an obvious comparison with Holocaust-denier David Irving here. Irving was a jerk, a fraud, and an anti-semite - but prosecuting him turned him into a martyr for freedom of speech, and gave his views far more prominence and credibility than they deserved. Prosecuting Mohammed is likely to do the same, with the added bonus of symbolising Australia's hatred of Muslims - something which is not exactly going to help in the battle for "hearts and minds".
Freedom of speech cuts both ways, and applies to views you don't like as well as those you do. Sheik Mohammed's views are vile and hateful, but they do not in and of themselves harm anyone. They are offensive, but giving offence is not harm. In the nineteenth century, the great liberal John Stuart Mill argued forcefully that
the sole end for which mankind are warranted, individually or collectively, in interfering with the liberty of action of any of their number, is self-protection
In cases involving speech, this is traditionally interpreted as "shouting fire in a crowded theatre". Sheik Mohammed's words simply do not reach that threshold. If people do not like what he is saying, then they have a simple response: argue with him. But there is no justification in a liberal society to ban his words or punish him for them.