You see all booksmarks that are available to you automitcally, and I don't think you can disable viewing bookmarks that have been shared.
It sounds like users are always clicking the 'Share Bookmark with Other Users'. You could get users to unselect this setting for future bookmarks and unshare the current bookmarks that are not needed by all.
To limit the bookmarks to only those of the current user, select the 'more...' item under the 'bookmarks' menu. Then select the 'My Server Bookmarks'. It may take a couple of extra steps, but this should display the list you want.