I hadn't heard of the Principles of Policing
It does seem to carry some unintentional irony these days, which is probably why we don't hear about it much. The first principle contains a clue as to why the Metropolitan Police Constabulary was founded. Its purpose was to break up the "London Mob" and arrest the ringleaders so that they could be tried for sedition. The government was rather worried about the London Mob, and had been considering deploying troops onto the streets, with all the attendant problems that would bring.
But, contrary to what the government thought, the London Mob was not a shadowy movement, causing outbreaks of rioting and looting with a view to revolution. It was in fact a phenomenon caused by dire poverty. In any given street, there would be many people who were starving, but also food aplenty. If one desperate person broke a pane and began grabbing food, or someone knocked over a baker's tray or apple cart, most of the street-dwellers would join in, and things would develop from there.
The so-called London Mob was eventually stopped by some of the first social security measures, which were brought in at around the same time as the Police. These eased the poverty at the bottom of society, and gave them a benefit that they stood to lose if they were caught rioting. Of course, the Metropolitan Police were ones credited with "curtailing the London Mob".
The purpose for which they were founded carries through to this day. A demonstration carries a threat to public order and the State - it will be well policed. A burglary carries no threat to public order or the State - you may not even see a policeman as a result.