Geek culture is and always has been mainstream culture in one form or another; it was never about rejecting mainstream culture but obsessively focusing on some aspect of it.

Hmm. I'd argue that it was more of the nooks and crannies of mainstream culture. Comic books, video games, science fiction television shows, pen and paper roll playing games. They were a part of pop culture, but they were never the widely embraced, celebrated part of pop culture.

What's really lost in the sands of time, though, is when geeks started becoming positively snobby as a rule. There's been comic book snobbery for a while: Comic Book Guy was a 90's creation, for example, but you have earlier examples like when the early comic book industry stopped publishing their romance lines in the Golden Age. But now there's a rule to attack women and other such "normies" as if they were this existential threat.

The snobbery that you bring up is part of the problem. They're creating an us vs. them barrier. That barrier, now more than ever, is being broken down and a lot of the hardcore geeks are really starting to feel threatened. The things that they used to escape, to feel safe, is no longer theirs to call their own.