Orac posts a defense of free speech for the Holocaust deniers, and I can't fail to link to it. As much as I despise the phenomenon and its followers, I think it should not be illegal - even in Germany. There are all kinds of both ethical and practical arguments to be made for this proposition.
I also fully understand that there are some good arguments that can be made for the opposite thesis, and I respect that. There will always be some limits on the free speech, and where one stops is quite subjective. I, for one, support the limited ban on Nazi symbols (depending on the intent of their display), while Orac argues against that too.
In the age of the Internet it is useless to ban Holocaust deniers' writings. It is much more effective to debunk them, to show that they're based on lies, misinterpretations, misrepresentations, omissions, stupidity and bigotry.