Thank you for writing about this -- and for drawing the connection with parasocial relationship dynamics and the entitlement and identification that sometimes comes with it, which I think really does help explain a lot of intense possessiveness I have seen in fandom cultures before that I couldn't really understand. I've often kept my distance from fandoms (despite sharing a lot of nerdy interests with them) because the hostility to competing interpretations of a character or various ships or just a sense of pervasive gatekeeping really puts me off; I don't understand why it can't just be about sharing in the fun with other like minded people! It should be a relief and a joy to find folks who share your passions and want to talk or even debate about them, right? But I think you have nailed why it happens. People who have a deeply invested, long term parasocial relationship with a property feel like they have earned that bond and that the bond is special, and so having tons of new fans or fans with different views claim that same bond can be threatening to their self-concept. I think people also extend this to the community itself as well -- they have a certain status within a particular fandom and they want to keep it; it's their family! Parasocially and socially.