THE brutal murder of 12 people at the offices of a satirical magazine in Paris today appears to have been carried out by militant Islamists. If so, many will again question the compatability of Islam with secular-minded, liberal European values. Mistrust of religion is not confined to Islam, but Europeans regard it as more threatening to their national cultures than other faiths (or indeed atheism), according to a 2013 poll by the Bertelsmann Foundation, a non-profit organisation in Germany. The threat of Islamic terrorism is rising, to judge not just by today's slaughter but also by other attacks and a recent upward trend in arrests for religiously-inspired terrorism reported by Europol, the European Union's law-enforcement arm. Perceptions can easily run ahead of reality, however. There were still more arrests for other types of terrorism (motivated by separatism, for example) in Europe in 2013, the last year for which pan-European data are available. And European publics wildly overestimate the proportion of their populations that is Muslim: an Ipsos-Mori poll in 2014 found that on average French respondents thought 31% of their compatriots were Muslim, against an actual figure closer to 8%.