[nickserv]

> Do not need to deal other non autonomous devices while in flight.

In a decent-sized city, there will be low-flying helicopters for police, fire and medical emergencies. Admittedly, this is much less common than for autonomous cars, but any slight problem could easily become catastrophic (no such thing as a fender bender in mid-air).

> Do not need to follow existing road traffic rules.

But do need to follow existing air traffic rules. New regulation would also certainly be drafted (one would hope anyway).

> Lot of paths available.

Maybe, again depends on regulation. Commercial airplanes do have certain "lanes" they are supposed to stay in, and are not allowed over certain areas.