Have you thought this through fully? In that case who'se supposed to be doing the arresting and killing? -- more ordinary people.
Look at what happened to Ceaușescu for example. He went from being confident in his rule to dead 24 hours later.
Yes, ordinary people have famously never killed tens of millions of civilians/undesirables at the orders of the government. Great point.
[dead]
Robots. That's why they're obsessed with AI and robotics.