tmande2nd said:
People get too attached to their beloved faves and mediums.
OMG HOW DARE YOU NOT LIKE X I LOVE X SO BY EXTENSION YOU MUST HATE ME!
HOW DARE YOU NOT LOVE CHARACTER X I LOVE CHARACTER X AND WRITE FANFIC YOU MUST HATE ME AND MY WORK!
I think this captures the underlying logic (or anti-logic, whatever you want to call it) inherent in fanboyism.
When people become exceptionally attached to a certain product, be this a movie, a video game, a band, etc., the significance of that product becomes elevated to something which is deeply personal. They associate this inanimate 'thing' with their individuality - thus, to insult the 'thing' is to insult the individual.
An interesting example of this can be seen in cases of road rage - people who place bumper sticks on their car (and therefore personalize their automobile, making it, to a certain degree, an extension of themselves) are far more likely to get aggravated by the actions of other drivers. If somebody cuts them off, honks, etc., they take this action not only as something rude or inconsiderate, but as a personal attack on their person.
The same thing happens when an individual who is heavily invested emotionally in a certain 'thing' sees somebody lambasting their preferred 'thing'. They get defensive, which inevitably transitions into hostility - they don't see somebody expressing their opinion, they see somebody openly attacking a part of them.
And yes, absolutely, someone becoming needlessly defensive and antagonistic towards someone who shares a different opinion than them is totally pointless and an utter waste of time.