The problem isn't that nerds became shitty people - it's that shitty people became nerds. Esoteric subject matters drew together a bunch of shut-ins that finally found a place with people they could relate to while still staying within the confines of their social inabilities and this created an echo chamber over the course of 35-45 years, depending on who you ask. However, with social media evolving more and more these days and any number of practically infinite subjects becoming highly accessible to anyone with a stable internet connection, you have people "encroaching" on what should just be, well, general subject matter that anyone can sink their teeth into. But, surprise surprise, said echo chamber gets pissy that they're "taking away" the one subculture that allowed them to remain reclusive and hobbyist over shit that shouldn't be put on as large a pedestal as it is in the first place - see how defensive a handful of gaffers get when an Off-Topic thread tries to criticize Japanese culture, for example. And, again, pop culture isn't stealing nerd shit from nerds - it's just making it more accessible for both parties to enjoy. The problem is that the caustic echo chambers of nerd culture that festered for decades just ended up exponentially worsening the capacity for the "original nerds" to be willing to open up, change, develop as a person, etc.
tl;dr it's forcing the figurative (and occasionally literal) basement-dweller to go get some fresh air, and the thought of their precious animus and Buzzcut Shooter 6: Hetereonormatives Save America (Again, For The Last Time) and whatnot being put in the limelight terrifies them.