Hell no, thats why its totally reversible. Once you are imprisoned you can just type /pplocate and it will give you the location and world of your pearl (if it cant find a world position for it you are freed, no logging out with the pearl!) after that you can go and find it and destroy it to free the imprisoned player. Giefers sometimes imprison as many as 10 players during a raid, but they are almost all free by morning thanks to the world of other players. Using citadel to create reinforced vaults (diamond reinforced obsidian must be broken 1800 times, thats quite while to mine through, put a chest with a peal inside of that to help prevent escape) is how griefers are kept in, but if a group of players with the resources wants to free another player they can all work on the reinforced blocks at the same time and cut the time down by orders of magnitude, a group of 20 can break a prison in minutes as opposed to hours upon hours for an individual.
The server was in quite the sate for a while, raids every night cities in ruins. But I held fast to non-interference, regular players had every advantage except organization, except the societal structure they needed to defend themselves proper. To save them from having to create that most essential part of society would defeat the point, so we freed our friends without admin powers and kept up the fight and now, we have won. Its hardly 2 hours before most griefers are imprisoned and held for trial, and less than that before those illegitimately imprisoned are freed. The players stepped up to the task, they managed to create order and stop violence. I have people complaining that the world is now too peaceful!
I don't interfere, even with I or my friends are imprisoned, even when I know there is a band of griefers heading for a city, I work very hard to remain neutral, and it really means i dont play too much anymore, but now I am pretty confident that shaking this order would be difficult. When players join they are spread far and wide, resources are difficult to acquire, so if a group of new grifers join it would take them hours to reach a city, at which point they would not stand a chance against the enforcers wearing such powerful enchanted armor that its worth more than the total income most players make in their entire Minecraft game, one or two of the incredibly rich citizens of the AnCap city have enough resources to single handheldly defeat a band of 20+ griefers.