I appreciate the sentiment but if it's ok for one person to visit the FD in flight then surely it must be ok for anyone to visit the FD in flight? Where does it end, and who should and who should not be in the FD?
For me it's easy. Operating crew only. No exceptions. Although some may believe these rules are to keep civil servants in a job I believe that is very wrong. A sterile cockpit keeps Me, my colleagues and my passengers safe. Long may it continue.