I would prefer that the jumpseat be for flight attendants only.
I will relate the following partial event that happened when I was jumpseating...basically I was the jumpseater standing around in the back galley during boarding with the galley fa...both lavs are occupied and people are in the aisle...when all of the sudden a passenger comes back gasping for breath and starts to collapse. The working fa is now struggling to get the pax into a jumpseat, I am pushing curious people back and yelling at them to leave so I can get to an 02 bottle. The working fa manages to get the pax into a jumpseat while I'm on my knees grabbing for a bottle and yelling at people to move out of the area. ...the situation went on and on, but basically the 'jumpseater' stepped in and saved the day. Passengers come back to the galley and collapse more often than you think. What would you do? A fa jumpseater would don gloves and jump right in to help, furthermore, they would know what to do.
You know this industry and you know that the galley areas are work areas and often times the only place we have to work on reviving a person, resolving disputes and handling many other events that take place. These events may not happen every flight, but when they do, we only get one chance to get it right or someone could be injured, hopefully not fatally. From my perspective, the last thing I want is to have someone standing around taking up space. It is safer for all concerned if those persons whom occupy an "unused" jumpseat are those people whom actually work in that area. If I need help, I want to be able to say, "grab an 02"...I don't want to have to explain where it is located. I'd like whomever is back there to have a general sense of how things flow in an emergency or prep or medical event because time does matter.
I'm sorry that the rules don't allow for what you see as a simple courtesy, but I believe the reasons for it come down to safety. We are trained to stay in a zone of safety, having non essential personnel in the galley creates a distraction and could negatively affect an outcome that needs to end on a good note. My having to tell you to do something or how to do something if you were jumpseating is very different from having a fa jumpseater telling me during an event what they are doing (calling medlink, captain) and my immediate understanding of what they are doing and why.
I hope you will understand.