Oh come on, people like First Order because of the cool white armor and the fact that people like bad guys in scifi shows, you don't really think it's popular because of fascism? I've hated fascism all my life, I've been against right-wing politics since I knew anything about politics, and still I find the First Order, Darth Vader, Kylo Ren - all that - very cool. I don't see any symbolism there, it's a made up faction in a made up world. "Propaganda merch"? :D Lol.
It's like saying Diablo fans like it because of satanism, lol :)