It's a slippery slope towards an Orwellian government.
I agree with you that ideas have consequences.
However, History is not a juridical object. In a free country, it is the job neither of Parliament nor of the judicial authorities to define the historical truth.
Everything requires balance. At one time, in America, ones exercise of free speech could, and sometimes did, result in a duel. Today, such matters are supposed to be settled by the courts but obtaining justice is slow and expensive.
The result is that things have evolved to the point where even our media seems to feel free to say just about anything it wishes.
Such abuses present a greater threat to the freedom of speech than the action of the German court, in this case.