There are foundamental differences between cars and planes.
Airliners are operated by very few professionals.
Cars can be operated by almost anyone over 18.
Basically, a driver has the liberty of driving like an idiot all he wants. You can drive several years without seeing a single policeman (and handing him your papers).
So obviously, the accident rate would plummet if you had self driving cars. But it would also plummet in a very similar fashion if all cars were operated with the same standards as airliners are : 2 drivers with 200 hours of practical training, years of experience, an operating manual to rule everything, regular and exhausting training in the sim, an other crew member to monitor what you're doing and pax to complain of the slightest problems...
The only question is : do we need self driving cars ? No, driving is not terrifying, it's actually already very safe.
Do we need self driving planes ? No, it's already even safer.