The thing for me is that originally the model was for investigative journalism. So, say some politician has some sort of rumoured corruption, putting someone undercover to find out whether they have their hand in the cookie-jar is right and proper. That said, the key thing is what is supposed to happen next. The reporter returns with their story to their editor, producer whatever who then kicks the tyres (legally speaking) to see if its safe to publish. Once it goes public, then an actual enquiry can be started because there's essentially not just public interest, but a trail of evidence -likely backed up with supplementary discoveries- for the appropriate authorities to work with.
So, when we're talking about internet "exposure" squads who go straight to social media with their findings, we're looking at an equivalent with potentially a lot fewer checks and balances. I'm not saying it can't be done properly, but let's be honest who knows how diligent these guys were.
The Activision thing seems wholly dissimilar to me, as much as anything as we're talking about an organization being investigated for a pattern of abuses. Which means that every detail counts towards producing the narrative that there's something deeply rotten systemically. Obviously this means that many of those details may be distasteful, but not rise to the level of anything legally punishable and yet still get prominence in coverage.
Doing something tacky like calling your party space "the cosby suite" isn't illegal in any way, shape, or form. How "bad" or "tolerable" it is to the employer depends somewhat on proximity or the perception of such (was it on the premises, during standard business hours, etc). Soliciting a minor for sex is however a whole other thing because irrespective or where or when the act occurred, that's straight-up criminal and time and place really don't enter into it.