Tribs looting all outlanders (say) because ONE outlander full looted them or one of their friends.
Odds are, the outlander who they just full looted wasn't a full looter himself, so what they did is no better than what the offending outlander did. And of course, if you apply the logic they just used, it justifies other outlanders looting all tribs (which, incidentally, is what caused them to loot in the first place). Spot the vicious circle?
You can replace outlander and trib with pretty much any cabal pairing, but it is probably the same dbags who are acting this way whichever cabal they happen to be in, just like the cowardly gankers who won't fight a remotely even battle tend to be that way whichever cabal they happen to be in.