In the US, the constitution is a document that delineates the power of the government, and also lists some of the rights the people have, which the founders thought important to list (and later amended as circumstances warranted), and our founders got to start with basically a clean slate. This is not true of European countries, where power was long held in divine monarchies, and rights had to be won or negotiated. Their right to free speech took a different path, and may be more limited than in the US as a result.