People sometimes forget that Hitler was elected, and this election was (among other factors) possible because Nazis were spreading hate speech and violence directly on the streets. Once a certain amount of terror and propaganda is reached, you can stage almost any coup.For this reason Germany is a modern democracy that was designed deliberately with the failure of the Weimarer Republic in mind. One of the many concepts to correct this mistake is that democracy in Germany can defend itself. One of the built-in defense mechanisms is that the German high court can prohibit parties. Another built-in defense mechanisms is that hate speech can be restricted in order to make certain forms of propaganda less effective. The sharing of power is also much more elaborate in the German constitution than in older democracies.
By the way, if a totalitarian government would somehow grasp power in Germany and abolish certain parts of the constitution, then the new constitution would be void and every citizen would have a right to fight this new government. This right is in a sense more radical than the US right of bearing arms in a militia, but clearly influenced by it.
To cut a long story short, whatever you think of those speech restrictions in the end, they have not been put into place without thought.