Here's part of a theory I'm working up. It is incomplete, provisional, and probably totally screwy somehow. THAT SAID:
'Geek culture' is built to facilitate social interaction between folks who have (certain) problems with emotional understanding and communication. Structured socializing (RPGs, cons, (video) game culture) is big here.
You'll note that geeks famously argue angrily 'til they're blue in the face about the pettiest pop-culture bullshit on earth -- which edition of D&D or Star Trek is the best, did Han shoot first, what exactly is Joyce's 'word known to all men,' is Tony Soprano dead, who's the metalest metal band of all, do Harry and Snape belong together forever, etc. One possible explanation for this annoying phenomenon is that geeks line up this way (w/r/t such irrelevant questions) so they can have the experience of being on a team without the trauma of being picked (last). In other words: affinity groups consisting solely of sharing an opinion.
That's part of why you hear so much affectless bickering in your local nerd store (or online forum): the point isn't to win, the point is to assert membership in a group when other forms of assertion are inaccessible.
NOW OK, BUT LOOK: 'neurotypical' folks do the same thing, right? NOT QUITE. The key difference is that people in/of the social mainstream are able to maintain memberships in social groups whose binding material is vulnerability, empathy, and/or public affection. (Let's leave the weird formalism of organized polyamory alone for the time being.)
People who for some reason have been impeded in their attempts to join groups who actually share and risk things -- by internal or external forces/circumstances -- will associate themselves compensatorily along 'ideological' lines.
Hence: Team Edward. (14-year-olds are socially-maladapted by definition, because our society can't handle puberty.) Hence: down-the-ticket voters. Hence: soccer hooligans.
If someone's in an affinity group whose main characteristic seems to be that the members are constantly at each other's throats (rather than that largely-irrelevant official business draws people together to agree broadly, and then to share experiences/feelings, e.g. the MLA or the NRA) then something is being compensated for, and some social fact is being avoided (or going unrecognized).
(I count myself among the uglies, here, and I have juuuuuust enough wit to hate it, but no more.)