^Can you imagine how deadly the skies would be if there was even %10 of the amount of traffic as on the ground?
There's a lot of room up there. There could be 10x as many small planes as there are now, and everyone would still have plenty of space. Instrument flight might congest the controllers a bit, but basic visual flight----which is mandated under Sport Pilot rules, the easiest level to reach----wouldn't be a problem. Especially now that more and more planes have traffic advisory systems built in.