If everyone had to understand how carburettors, engines and break systems work; to be able to drive a car - rather than just learn to drive and get from A to B - I'm guessing there would be a lot less cars on the road.

(Thinking about it, would that necessarily be a bad thing...)

The problem is that we have a huge swathe of "mechanics" that basically don't know much more than how to open a paintcan and paint a pig despite promising to deliver finely tuned supercars with their magic car making machine.