While the events involving a stabbing attack on a British soldier in London are still shrouded in uncertainty, possible revenge attacks have also started. The grisly spectacle has quickly devolved into a violence-porn media chasing every possible rumor or story. Whether the attackers had some religious or political motive or merely were apolitical attention seeking sociopaths, I do not know. This does, however, illustrate one of the darker points of the current media cycle.
Compared to the USA, the city of London has become a virtual police state (although the Americans are rapidly changing that). There are CCTV cameras everywhere, privatized police/security, and strict gun (and other weapon) control laws. Despite all of these 'precautions,' a mad slasher with a knife and one unlucky victim managed to provoke such a media reaction (and public backlash). A grim "return on investment" for the price of a cheap blade would be millions of pounds worth of police/security/media coverage of such an event that feeds upon itself as the frenzy builds.
For all the fuss about an inaccurate, exploding 3D printed gun in recent times, the knife attack serves to remind that the equipment for disruptive actions (including violent ones) is rarely far outside one's own kitchen. Even with development of 3D printers, firearms, and ad hoc explosives vanish from the earth, a single edged weapon can still stand as an assassin's weapon, as it has for the sum total of human history. Why should the future be different?