That's a personal information database and making one without consent of the people detailed is _super_ illegal in Europe.

There's a few examples of entities like Jehovah's witnesses making do-not-visit lists that have been considered as a personal information database and such have been in hot water many, many times about that. Yes, even though you might do them to help you personally, you're acting as an agent of the org you're associated with, and such you're not supposed to be doing that.