As with most defenses of speech, the issue is not solely what this person said, but whether another's speech may also result in prison. Incitement to violence is speech that should be sanctioned, as should defamation and fraud. Hate speech, including the denial of events that clearly occurred, should also be sanctioned, just not legally by imprisonment, in my opinion. If by some twisted logic this guy is viewed as a martyr by some, that is further reason to respond to him with ridicule, rather than jail. If, outside of the incitement language, others act because of his words, they should be imprisoned for their wrongful ACTS, not the thought or hate that inspired those acts.
Last time. Streicher walked nobody into the gas chambers. Yet, he was convicted at Nuremberg. If you want take issue with the Nuremberg trials, that's a big piece to bite off.