If there were 25 million active GA pilots...

Navigating and controlling a vehicle in the air will always be more complex
than moving over the ground. In my opinion, that eliminates the possibility
of the masses taking to flight. Perhaps it will be possible with advanced
navigational technology and more efficient and more controllable propulsion
some day.

Compare driving a car to piloting a boat: still two dimensional but much
more difficult in terms of navigation when the boat is on open water away
from land. Weather, finding fuel, sinking, capsizing, grounding, and
drowning are serious hazards. Navigation is done with charts, radar, GPS...
many of same tools air pilots use. None of which is necessary in a car on
roadway systems - except in the
boonies. There are no brakes either; but you can stop when you want,
assuming you have enough room and can use reverse propulsion.

Now throw the third dimension on top of that and remove braking (except for
rotorcraft). Now the pilot workload goes way up becuase control and
navigation in the vertical dimenstion have been added. And the same hazards
are still there - OK, replace water hazards with gravity hazards.

Even in a boat, there are often marked traffic lanes in high-volume and/or
shallow waters. Until we get highway-in-the-sky HUDs for general use, we
only have nav instruments - much more demanding to learn and operate than
any car system.

I don't think moving through a fluid (surface boat, submarine, aircraft)
will ever be as simple and as popular as moving over the ground.

-Scott