Freedom of speech is essential. Only in the light of this type of freedom we can rationally evaluate evidence, reason about it and progress in all types of knowledge. We were extremely lucky to get such a complicated language in the course of our evolution, and it is the reason we are where we are now. If we wish to progress even better and faster, we need to allow for all ideas to come to the forum of thought and have a say. Only there we can judge them based on evidence and logic.
This is why I tremendously enjoyed Christopher Hitchens’ vigorous defence of this freedom.