Excuse me, but a comparison with Hitler is IMO a bit strange. Hitler killed millions of people and did so much damage to my country that generations afterwards can still feel it and are still feeling guilty, even those born after the war (like me).
The world is full of crazy people who want to kill other people, sometimes because they hate them, sometimes because they are really psychotic. Look at all those killings in the US, and it happens everywhere. I understand that harry and Meghan were threatened.
Those prominent royals have to be protected even if they are not favourites of many. I wonder if Fergie and her daughters and other members of the family get protection which is paid by the taxpayer? Where do you draw the line or the limits?