In my view as a long-time moderator, the purpose of moderation is conflict resolution and ensuring the sitewide rules are followed. As reported today by !vegan@lemmyworld, moderator Rooki's vision appears to be that their personal disagreement with someone else's position takes priority over the rules and is enough to remove comments in a community they don't moderate, remove its moderators for the comments, and effectively resort to hostile takeover by posting their own comment with an opposing view (archived here) and elevating it for visiblity.
The removed comments relate to vegan cat food. As seen in the modlog, Rooki removed a number of pretty balanced comments explaining that while there are problematic ways to feed cats vegan, if done properly, cats can live on vegan cat food. Though it is a controversial position even among vegans, there is scientific research supporting it, like this review from 2023 or the papers co-authored by professor Andrew Knight. These short videos could also work as a TL;DR of his knowledge on the matter. As noted on Wikipedia, some of the biggest animal advocacy organizations support the notion of vegan cat food, while others do not. Vegan pet food brands, including Ami, Evolution Diet, and Benevo have existed for years and are available throughout the world, clearly not prohibited by law in countries with laws against animal abuse.
To summarize, even if you don't agree with the position of vegan cat food being feasible, at the very least you have to acknowledge that the matter is not clear-cut. Moreover, there is no rule of lemmy.world that prohibits those types of conversations unless making a huge stretch to claim that it falls under violent content "promoting animal abuse" in the context of "excessive gore" and "dismemberment".
For the sake of the argument, even if we assume that the truth is fully on Rooki's side and discussions of vegan cat food is "being a troll and promoting killing pets", the sitewide rules would have to be updated to reflect this view, and create a dangerous precedent, enabling banning for making positive comments about junk food (killing yourself), being parents who smoke (killing your kids), being religious "because it's not scientific" and so on. Even reddit wouldn't go that far, and there are plenty of conversations on vegan cat food on reddit.
Given Rooki's behavior and that it has already resulted in forcing the vegan community out of lemmy.world and with more likely to follow, I believe the only right course of action is to remove them as a moderator to help restore the community's trust in the platform and reduce the likelihood of similar events in the future.
Is this all over a disagreement on whether a cat can survive on a vegan diet?
That is my understanding based on Rooki's own post, the post of the demoted vegan mod, and the modlog containing the removed comments.
Here's the thread (archive link) that the admin intervened in:
Edit: This was in-between the comments by @[email protected] being removed/restored
Also to add Rooki is an admin of LemmyWorld.