I don't think your comparison makes sense. A motorcycle is not broken without a rider; it is not being used to move from point A to point B, but it is capable of being used to move from point A to point B.
A broken motorcycle is not being used to move from point A to point B, however it is not capable of being used for that purpose. The broken motorcycle is clearly at a lower state than a functional motorcycle.
Perhaps a comparison that works would be (a broken motorcycle + a rider) is as worthless as (a working motorcycle + a broken/ignorant rider).
Neither can be used to move from point A to point B without the addition of their missing component.
If we assume I have the appropriate skills/training to successfully operate the motorcycle that is missing a rider can we not just as easily assume that I have the appropriate knowledge/materials to add the missing screw?
E: The point I'm trying to make is that it is the same scenario. We could argue over which assumption is more practical (how hard is to to find and install the screw vs ride a motorcycle) but that is a separate point.
The screw seems most important when it is the 'weak link'.
But the same is still true of all other components.