A disruptive technology has arrived from the U.S., in the form of the taxi app Uber, to threaten the protected markets that have allowed European cab drivers to keep fares high and competition low. It was no surprise then that in London today, thousands of the city's iconic black cabs snarled up traffic in Trafalgar Square to protest. They're Luddites, right? Well, "Up to a point, Lord Copper." London's cabbies have some good arguments.