If seen on a massive scale, I'm not so sure about some these arguments.
Air transport will need management for safety reasons, which means air corridors, landing areas, some kind of ATC system. Which correlates to infrastructure costs, not so straight line transportation and not so time efficient commutes.
As activity centers tends to be somewhat concentrated, huge amount of flying cars will tend to go or left small areas at the same time, creating air traffic jams to land or take off.
Classic infrastructure will still be needed to transport heavy items, such as large quantities of food, machinery, etc. Even the construction phase a new developments will need those roads and bridges.
Strangely, faster transportation doesn't mean shorter commutes, quite the contrary, the average commute time tends to go way up when transports evolve to become faster and denser as it enables urban areas to grow even more. The real alternative is to "de-concentrate" activity centers to have relatively autonomous parcels with residential, work and commerce close together and necessitating only light transport forms (by foot, by bike, or light transports like tramways).
Flying cars are also mostly "fail catastrophically systems", it's good that motors are redundant, but there are not the only items that can fail. Batteries, the control surfaces, the inboard computer, or the whole structure can fail. Flying is also quite hard, specially in difficult meteorological conditions, building automation to handle such cases will be extremely hard (I've no competences in the area but the picture of a vertical landing in windy condition, seems a bit frightening).
Interesting statistic: on a per journey basis, airplanes have 2 to 3 times more death than cars, (on a per km basis it's very safe), imagine what it would looks like with a lot of small commutes.
I'm not convinced it's really the solution... I see it at best as a cheaper and more accessible helicopter ride.