Why should I believe a scientific paper or textbook?
You don't have to believe it. If you choose not to believe the source, that's fine, but we have a policy on what sources we consider reliable. A few fans of a TV show is not on that list.
If you disagree with Wikipedia's definition of reliable, you should try and get consensus to change it. Until you do, that's the definition we go by, and by that definition, a scientific paper is reliable, a random fan of a TV show is not.