Notice that the bad guys in the castle sets are now non-human (trolls, skeletons) too ?
Anyway, I like to think of the SP3 guys a bit like the Peacekeepers in Farscape. The 'Peacekeepers' are the descendants of humans kidnapped from Earth thousands of years ago & genetically engineered to become the police for a distant section of space ... unfortunately their bosses died out (kind of) & they were left to their own devices. Which didn't work out too well for everyone else; they became overly oppressive and violent, suppressing any dissent and basically acting like a bunch of fascists. :-)