I think stealing or plundering oow is lame. If you are fighting a kingdom, whether hostile or war, you don't want other kingdoms interfering with your conflict right? So to be fair you shouldn't be able to hit other kingdoms either.
I agree 100% with you on this - to many tag HOSTILE STFO but they're happy to do randoms of their own. Only reason why we did OOW plunders in this war is because BOB attacked us during our EoW cf with WS