It's not a silly question, and is fair for an internet debate. It might be the case that there is an even better argument for the use of professional driver trainers rather than parents when learning to drive, and if you asked most driving instructors, they would probably agree.
Learning is a fascinating thing. We learn by watching, doing, and thinking. For most of us, we have learned a lot about driving before we ever get behind the wheel. Watching what is happening, implicit learning is teaching us something, although it may also be teaching us the wrong things at times too. When we learned to walk, we watched, tried, and eventually succeeded, helped along by a little bit of evolutionary development with some of the predispositions to learning to walk built into us.
So going back to the car, we have picked up a lot of what is going on implicitly, but we are not prepared evolutionarily to cope with it. Anyone who has tried to teach their teenage son/daughter about braking distance quickly realises that brains are only hardwired for speeds up to about 20km/h, and that learning to judge speed and distance required to stop takes a lot more training.
Step into an aircraft, and most of us have not had the benefit of a decade of implicit learning, and most of our evolutionary processes start working against us. Speed, height, complex depth perception, moving in 3 dimensions, even multitasking is more than a little foreign. Some may have even grown up reading Biggles books or playing flight sims and have a lot of implicit learning which actually has already set some bad habits in place in terms of expectations. I had a friend who was a driving instructor, and remember him commenting on teaching people to drive. It wasn't that difficult, he said, except when you were tasked with teaching someone who had recently immigrated to this country and had not grown up around vehicles. The act of learning to turn a steering wheel and equating that to changing direction was just one thing that they didn't "get" straight away, let alone all of the other concepts.
So the question of whether we need an instructor or not is very relative to the amount of implicit learning you have, and in the real world, greatly related to the potential consequences of getting it wrong. As I said, there is a really good argument for using a driving instructor rather than teaching our kids ourselves, and this is reflected (in Victoria at least) by the fact that a learner needs 120 hours in the logbook, but 10 hours with a driving school can be counted as 30 hours in the total. Without being a flying instructor, I suspect that a lot of what they are taught is how to cope with unexpected situations and to provide an environment where a student can have the opportunity to break down complex, unnatural tasks into discrete, manageable ones so that the student has the opportunity to get the learning bit done with much lower risk of it all going wrong.