Fan can be fanatical...
But what I find interesting is the business behind fandom and kpop...everything is marketed to sell an "ideal/romantic boyfriend or a hot bad boy" for BG or a "sex or cute doll" for a GG, with a pretty and addictive packaging (song with catchy sounds, aesthetics, gestures...). Thus the importance for these groups to be sold as single (and not "taken"). That's why you see idols talking with their fans and telling them they "love" them....in a way, it's like "courting".
The phenomena of sasaeng is quite telling. There is also this logic of possession and pride because of the idea of "I've had paid to have that and I've so much invested (financially, emotionally, a lot of time) in my group that I cannot be wrong".
This logic of addiction (developed through fandom) combined with the competitive mindset, companies are playing with that to have a reliable source of money...
Perhaps for some groups it is more subtle but down below, I think it always comes to that...
lol basically Kpop is at the same time a poison and a drug, exploiting the desires of its consumers (and the narcissic dream of glory and celebrity of its idols) or creating new needs.
I sound very pessimistic, isn't it ?