Those are not my concern, my concern is larger guilds using it to protect them selves from PvP and for them to grief individuals or smaller guilds. The only way to fight these zergs that wont come out to PvP untill they have 2 to 3 times your numbers is to get them when they arent ready.I think Blacklisting as a function was harmful only because the system was incomplete. Such a system cannot and should not be attempted without realizing the vision in its entirety. Blacklisting was incredibly useful for giving guilds the ability to exert dominion over their claimed territory and for dealing with griefers, thieves, and enemy blue-flagged meat shields. It was also useful for securing resources rights in their area by targetting non-guild miners and non-guild farmers and woodcutters.
That said, a function that was missing was the ability to toggle, codify, and in effect make your own laws, and elevate your own people to that as enforcers of your guild's law. What sucked was having your guild have to abide by Tindremic or Khurite Law when in effect you owned the town. But even if you owned the town, attacking or dealing with random blues, thieves, etc, or even hitting an NPC or a pet would flag your own men grey, to be targeted by the local guards.
That is what was harmful, the inconsistencies, flaws, and incomplete design of the feature itself, not the inherent concept.
One major flaw is that they can target member of a enemy guild one at a time in town with black listing. If the 10 man guerilla force is defeating the zerg then they could just black list the stronger players or the leaders to cause the group to break up.
Having laws to "complete" the system doesnt adress the issues of the systems for the people getting targeted by the bigger guild.
If they were going to have a system then the guards shouldnt be involved in the fighting. Either just allow them to turn off guards which still has the issue of zerg massing up force before hand and then leaving/logging when they dont have the zerg on anymore. Or have war decs. War decs if allowed agaisnt a individual would allow what ever keep owner the ability to protect their town with out having guards protect them. If they are strong enought to get a keep then it should not be a issue for them to protect the city. You could even give them war dec discounts. You will then have players protecting towns instead of guards protecting the zergs.