No idea what the average age on this forum is, and it's not technically a celebrity, but I can remember when Scientology used to be seen by most people as just being one of those weird religions that movie stars get into for some reason. I mean, the information that brought them down was already out there, and the public had some vague idea they were a litigious UFO cult with a few skeletons in their closet, but the general impression was that it was something similar to the Hare Krishnas or Transcendental Meditation. Bizarre and maybe kind of sketchy, but not to the point of deserving any real attention. South Park putting both their ideas and practices on blast at the same time, and on a major television program that millions of people saw, played a major role in turning public perception firmly against them.
I doubt that Chanology would have ever gotten off the ground had it taken place before that episode rather than in 2008, or that it would have gotten into the spotlight if it did, as opposed to languishing in obscurity and being framed as "the hate group known as 4Chan attacking the websites of a controversial, minority religious movement", with most channels focusing on factoids about Tom Cruise. Scientology wasn't exactly thriving before the episode, but it lost all public legitimacy almost overnight.