The administrators of MangaDex want(ed) to keep its fora from turning into yet another political battleground, and didn't/don't want scanlators to include pages that were political incitements in one way or in another.
There has been some snarking that the administrators already allow the names of scanlation groups to bear political messages, but that point only argues that other groups should be allowed to do the same, not that other modes of expression should be accepted.
By the way, one of my own comments was “moderated” under the policy; it is not as if I am apolitical or somesuch.