Political demonstrations are frequently controversial. Any issue that can mobilise tens of thousands of people is likely to involve fierce passions, and provoke strong reactions. In a democracy, those are insufficient grounds for a ban. That is why the Metropolitan police have resisted ministerial pressure to withdraw permission for a Palestinian solidarity march in central London this weekend. Sir Mark Rowley, the Met commissioner, has taken the view that Saturday’s march does not pose a threat to public safety. Downing Street has very reluctantly, and perhaps only temporarily, deferred to that judgment. Rishi Sunak has expressed his objection in terms...