It's a Hexbear rule from when /r/vegancirclejerk was going to move over here en masse expecting a ban on Reddit, and didn't end up moving over. And also didn't get banned on Reddit.

However, it did cause a whole bunch of people getting extremely mad at each other, and this was the compromise: vegan gang sticks to calling everybody else bloodmouth carnistremoved murderers only on their vegan communities, and everybody else is banned from vegan communities but adds content warnings to posts that talk about food. We have lived in harmony under these rules for many years now.