Been reading this one with some interest and have come to the conclusion there needs to be a 3rd option. Obviously this is never going to happen but I would be interested in comments.
Here are some rough thoughts on the what should be the definitions:-
Request = Something nice to have which if refused does not result in any increased risk to safety) Eg.Level change for fuel effeciency or improved winds or light turb. Direct tracking for track shortening or to an approach fix. Rwy which has less track miles or taxi time to terminal.
Desire = my request should be granted as the current clearance/rwy assignment creates an increased risk to the operation of the aircraft. Eg Level change for mod turb or fuel burn reasons which if not granted may result in fuel exhaustion or diversion. The proposed rwy is within the performance limits of the aircraft but due to fatigue or other matters, safety is reduced. I am understand that I may be required to hold to fit into the traffic pattern to facilitate my desired RWY.
Require = my request/require must be granted. For example severe turbulence (passengers may be injured or the structural integrity or control of the aircraft is about to be compromised). Weather deviation (again passengers may be injured or the structural integrity or control of the aircraft is about to be compromised). Runway, the assigned runway is not long enough under the current wx condition using max autobrake/reverse etc. NB fatigue not a reason to use require. If the longer rwy is not available I will divert to my alternate or declare PAN/MAYDAY.