Countries like Germany have long criminalized Holocaust denial as well as the use of Nazi symbols. The problem is that such laws do not defeat unworthy ideas or theories. They merely force them below ground and give these people a status as victims. It also breeds conspiracy theories that they feed on in their recruitment campaigns.
An analogy can be drawn to the prosecution of religious criticism and criticism of homosexuality, here.
In the Czech Republic, you can go to prison for three years for uttering such theories. There is a reluctance to be seen defending Duke, who has led a thoroughly indefensible life. However, the West cannot claim to defend free speech while exempting certain unpopular or intolerable theories. It would be better in my view to allow good ideas to defeat bad ideas in the free market of speech.
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