It is, no argument there.
However if you were to advertise a "doors-off" tour and tell the customers that they were free to remove the seatbelt after takeoff and move about the open cabin to take photographs, my guess is that your FAA Inspector would be all over you.
The harness was obviously a risk mitigation and the FAA knew it. Now they're acting shocked.
That is precisely why open door flights should be banned for the general public unless seatbelts are worn all the time OR the FAA needs a new regulation that states that open door flights in helicopters OR airplanes may only be conducted when FAA approved harnesses are in use. Vendors will then produce harnesses with quick release tethers that are made to a (new) appropriate TSO and then just as seat belts need only meet a TSO they can be used in any aircraft when installation is signed off by a mechanic (or a pilot if deemed appropriate). Make removal and installation a minor alteration and be done with it.