A friend of mine is taking his wife on a European cruise that ends in Barcelona this week. He told me how much they love the Spanish city and how they’d normally stay an extra couple of days there before flying back. “Not this year,” he said, before stressing that they’re “gonna get outta there fast” because of safety concerns. We had this discussion before this weekend’s violent riots in Barcelona, in which hundreds of people (black clothing, masks, and Palestinian flags prominent among them) looted and damaged dozens of stores, injured at least 15 police officers, and set multiple...