If you tolerate banning the speech of others, karma will come back around and ban your thoughts and opinions. Maybes one day, as Germany becomes more Islamic they may make it illegal to say anything bad about the Koran.
You could lose your job from voicing your disagreement of religious texts and ideologies.
It's a slippy slope if you begin to ban free speech.
I think it is okay that we have this exception here in Germany just because of our history and for showing that we are aware of it and don't want to have something like this ever again. In fact we have many taboos here in talking about the islam or immigration. These are very sensitive topics here because of our history. But my impression is, that it's okay to treat these topics very carefully.