There’s a big difference between merely saying This movie sucks! and taking it out on the people who made it. When Star Trek: The Motion Picture came out, Trekkers were not screaming for Robert Wise’s head. Even the late Harlan Ellison wrote a polite, but negative review in Starlog. And this is the guy who often took potshots at Gene Roddenberry the way Stephen King hates on Kubrick.
Social media is the big factor here. It’s possible rotten fans may have always been with us. I imagine there were letters even Cinefanstatique magazine declined to print back in the day. There was that one SW blogger fellow who’s been blocked by Dave Prowse and John Williams on twitter for their behavior. Seriously, what issues could anyone possibly have with them?