Not sure about the autopilot part (even planes autopilots follow a flight path). I'm not an expert either, but with roads, there are clear lanes and markings. And ability to generally see around you, and judge distance.

Is what sets the lanes in the air are traffic controllers and flight plans? We're already short on traffic controllers. And there are already lots of near-misses (and not near-misses) even with the heavy regulation and control. Can't imagine having it as mass personal transit driven manually. There'd need to be a mass central system that controls everything, and in that case, might as well just keep it commercial

The energy efficiency isn't great either on personal aircraft

not an expert, just shooting the crap