If I have an access-controlled entry, and one of the people with access to that entry bookmarks it and gives it an appropriate tag, I would definitely NOT want that bookmark tag to be visible to people who do not have access to my entry.

A lot of the access controlled posts I write are very sensitive and I would not want cetain tags associated with my posts in places where they are visible to peole outside of my Circle. Even if the post itself is not visible, people would still wonder why I write so many posts on certain sensitive topics.

If the bookmark was visible but the tag itself was invisible, I would be comfortable with that.