In a word: DUHHHHHH!
Some people tend not to think so because they believe al Qaeda is attacking Western Civilization instead of Christianity per se. I disagree because Christianity (and Judaism, for that matter) played a major role in HOW Western Civilization developed in the first place.
This is the same type of mindset that got the EU their ill-fated 500-page constitution which doesn’t have any mention at all of Christianity’s historical role in it. When 23,000 tourists can jam St. Peter’s Square in a single day, that would certainly have the Vatican police (and the Italian military, including the carabinieri) on edge.