I cannot decide if we have invincible ignorance of history and human nature or an unshakable belief that “American exceptionalism” means that it could never happen here.
Suggested reading: "Hitler's Willing Executioners." The book focuses on the actions of Nazi Reserve Police Battalions (in the Army, like MPs) in Poland. These were not rabid SS or Gestapo, they were a notch above 4-Fs, drafted into service. Average age in their 30s, family men with children. When put in uniform and given orders to shoot Jewish women and children, they followed orders.
In a SWAT scenario in the USA, the SWAT snipers will deploy where they are told to deploy. Once one person fires a shot, they will all dump a magazine.