More to the point, the problem here is if it could be done by someone not authorized by the vehicle's owner, rather than by someone not authorized by Ford Motor Company.

If the vehicle's owner wants to modify their car's code, or pay someone else to do it, there are many legitimate reasons to do that and it's no different than the mechanical modifications that people have been doing since cars were invented.

As the potential buyer of the car used in a few years I want to know if it was ever run non stock, as most modifications trade how long the car will last for more power.

There is no way to know that. Someone could remove the entire computer, put it on a shelf, operate the car with a modified one and put the original back in before they sell it to you.

Moreover, this rule is about remote access, not what someone can do who has direct physical access.

Yup. In fact, I have a vehicle where exactly that happened. Bought a used diesel pickup truck. A year later it wouldn't start: ECU was completely unresponsive and wouldn't even send anything over OBD. Had it towed to the dealership and during their analysis they found an aftermarket torque chip in the ECU and removed it. Truck started right up after that.

If the dealer hadn't mentioned that, I'd never have known. I don't even know if the person we bought it from knew about it since he was the second owner.

Giving the vehicle owner an easy button to crash their car remotely is going to be a liability for the manufacturer when the obvious happens and it's used as murder weapon.

This makes zero sense. It's like saying giving the owner a steering wheel they can use to crash their car into a pedestrian is going to be a liability for the manufacturer when the obvious happens and it's used as a murder weapon.

That's ridiculous, the person who is liable for the murder is the murder, not the car company. It's a transparent excuse because they want to force people to have their car repaired at the dealership. Nobody's buying it.

There is a legitimate use for a steering wheel. The ability to remotely command full throttle on a car is useful for what?

It's a computer. There are many legitimate reasons for the computer to control the throttle, from implementing a top speed governor when the car is in the hands of your children, to tuning the engine for unusual environmental conditions, to interoperating with aftermarket vehicle modifications.

"Remotely" is just how the code gets installed. But installing updates for any of those features over the air is perfectly fine when authorized by the owner of the vehicle.

The ability to command the accelerator pedal is important for many diagnostics tests. Sometimes the car is on a dyno for those tests which makes it impossible for the car to know it isn't on the road.

This access only needs to be physical. There is 0 argument for providing wireless access to the accelerator. Physically plugging into the car for accelerator control or having someone work the pedal are the only methods that make any sense.

The computer can do diagnosis if it can command that pedal. Often better than physical access as the computer can get the exact rpm it wants.

Yes, or if the police can do it. That would also be a defect, IMO. There should be NO control possible of safety critical systems by anyone not in the drivers seat.