Take this post for example: https://www.reddit.com/r/northernireland/comments/1ll6ocg/see_it_say_it_censored_kneecap_is_not_the_story/
Speaking from experience, people in Ireland are overwhelmingly pro-palestine.
There is this user in the comments: https://www.reddit.com/user/EntireCourage308/
Its a nearly year-old account, it started posting about a month ago, it made some innoculous posts, then pivoted to posting far-right misinformation in the r/northernireland subreddit.
There’s loads of other accounts just like it.
Well, first off it can’t bhappen “to Lemmy” because Lemmy isn’t va site - it’s a piece of software.
It not only can and will but already has happened to individual instances. And they end up getting defederated by other instances and then either fix the problem or fade away.
And individual users can just move to other instances (or if they’re smart, just stop using or even delete their account on the problem instance and keep using their other accounts on other instances).
And through it all, the rest of the fediverse just keeps chugging along.
Which illustrates the key difference between Lemmy/Mbin/Piefed/etc. and traditional social media - the fediverse is flexible. Individual instances can and will and do come and go, and it doesn’t affect the fediverse as a whole.