I believe that if you declare someone and make aggressive actions towards them, you should be an open pk target to the organization the person belongs to. If, say, Kreaton is a suspect to me and I go and try to kill Glevich who's standing right next to him, Kreaton should be able to defend Glevich within context of the action at hand. The PK Suspect system should be there to defend people who are not pvp players or characters. However, for the side of the game that is a part of the pvp playerbase, Vengeance becomes a different tool entirely as the risk of dying is now simply a part of their career in the game.
Now, with the above example, let's say Kreaton turns off his pk careful to help Glevich and they both kill me, so I go and use the Avenger to have him exact Vengeance on Kreaton to kill him back. How does the situation constitute a punishment? Glevich and Kreaton are city mates and the theme for any organization is that one looks out for each other to some degree or another. This completely ruins the context of city commraderie because there is a mechanic in the game that would punish someone who does happen to pvp through declaration due to them abiding by the setting Lusternia has.
One might think that the people involved should just not pk openly and that openly pking someone should be removed entirely, but this isn't the issue. Open pk in a roleplay setting provides tension and story when it serves its purpose properly If Tridemon is causing problems for Magnagora in the Sea of Despair during the sea battle, then I go to stop him and he runs outside of enemy territory, I should be able to step outside the boundaries and kill him. I'll accept the suspect and I'm okay with that as it prevents me from just constantly hunting him down for no reason, which makes sense because the context in why I killed him is completely gone. However, if Tridemon is attacking Nymerya while she's working on something, I should not be punished for defending her based on the sensible action that took place prior.