I welcome them. This kind attitude is bad for the game and the community, and it’s ultimately self-destructive for the thing that you care about. Making an issue out of who is and isn’t a real fan drives away new blood and creates an ever dwindling pool of people who care the thing as the old timers filter out. You end up killing the thing you enjoy.
You shouldn’t have to read a twelve novel series to be allowed to talk about or enjoy characters. I don’t expect it from anyone. There are tons of fans of Jace, for instance, who have never read Agents of Artifice or The Secretist. That’s okay.
Now, if people are wrong, you can talk about it. Explain it. Welcome them and share your passion with them. Don’t belittle them as band-wagoners because they’re showing interest in something you like.