Yesterday a teacher was murdered in cold blood in the street in a Paris suburb. The perpetrator was an apparently religiously radicalised 18-year-old. He attacked the teacher with a long knife and beheaded him for showing Mohammed cartoons during a lesson on freedom of expression. He had tried to illustrate to his students by means of concrete examples what everyone has to tolerate in an open society. 

The perpetrator may have been spurred on by pupils and parents who had denounced the showing of the cartoons to the school management and on social media. These online attacks led to numerous threatening phone calls, as the headmaster reported. In the video of a protesting student, a man appears who is known to the secret service as a radical Islamist - and who is on the board of the Conseil des imams de France.

Nevertheless, other Muslims cannot be held responsible for the crime. But they can influence whether acts of violence are seen within their religious community as a legitimate means of enforcing demands, and whether other followers of their religion accept that freedom of expression is an essential good of Western states and that societal rules must be negotiated democratically.

After all, the Conseil français du culte musulman (CFCM) has strongly condemned the assassination and made it clear that "nothing, absolutely nothing, can justify the murder of a human being". This is an important signal. It is to be hoped that it was not just for tactical reasons. For when a 16-year-old French received death threats earlier this year, after she had previously posted on Instagram "I hate religion, the Koran is full of hate... your religion is shit", the CFCM chairman had commented: "She has insulted religion, now she must bear the consequences of her words".

Nobody has to like cartoons or agree with bawdy statements. But those who have not understood that one is allowed to be just as insulting about religions as about political beliefs or preferences for music or sports, have not understood the nature of liberal societies and are a danger to them. It is also up to Muslims to uphold these values and to stand up for them in private and in public.

However, social actors are also responsible for this. Parties and NGOs must not make the mistake of remaining silent for fear that condemnation of such acts will stir up resentment against minorities or that their statements will be instrumentalised by circles with their own agendas. Otherwise, we leave the discourse to religious extremists and to no less anti-humanist nationalists. It is to be hoped that those who, out of humanist conviction, shout "no room for the fascists" will also chant "no room for the Islamists" with the same clarity.

Background article on the crime on lemonde.fr