I wouldn’t call them fanatics, as it implies they have a deep emotional commitment to something. Instead I would put it down to a combination of naivete; a craving for the “good old days” of monarchy punctuated with a great loathing of their former nobles; an utter lack of understanding of why and how America came to exist, etc.
They desire unelected elites to rule, federalism among nations with people who have vastly different cultures, languages, and legal systems, the welfare state, and after 1500 years of almost continual war, they are terrified of it, and reject any reason for it.
It is like the fantasies of abused children who crave a normal life and abundance, and think that by superficially mimicking a healthy and happy family they will become one.