This is the meme comments, whether they are internet lore (a way to signify that you were there) or simply just in on the joke.
Community expectations.
Some communities are made to be in on the joke. Some communities are made to be informational and analytic. Even the latter communities will eventually have some jokes that occur, which over time will create a caste of those who are “in” on the joke.
Ethics and morals.
In smaller, usually hobby communities, this generally isn’t problematic. However in the wider internet, it’s not uncommon for hate to be the joke, and spreading it being “in” on the joke.
Therefore, the hivemind is not inherently bad, as it is just a nature of community expectations that are connected through shared experiences over time. But just like we’ve seen through history, this can be pretty easily manipulated and people who don’t have humanitarian beliefs in mind perpetuating that rhetoric.
In any case, to combat this, I think the community just needs to set specific expectations. GameFAQs forums would be a great example of having mostly problem-free hivemind, as video games have a specific meta-game that is developed over time and jokes from that shared experience (git gud, don’t get hit, etc). The whole point of these forums was to talk about the game, from meme (before memes) to painstaking min-maxing, and the discussions of the community would revolve around this. The rules of the forums made it pretty hard to be overtly mean or engage in discussion that wasn’t centered around the goal of the community.