Mainstream marketing has already happened. Look closely at commercials for "active safety", "lane departure prevention", "collision prevention assistance", "lateral collision avoidance". They are phrased around the event that is prevented (lane departure, forward collision, lateral collision), not the mechanism of prevention (autonomous steering, autonomous braking).
>> "... you, the driver, will have to be ready to take over should its operating system go all Microsoft 'blue screen of death' on you."
Driver re-engagement is a major problem we[1] are running into. Until cars can be fully autonomous on all roads (say 2025), the driver must keep the driver ready to re-engage as necessary. If the car sees (vision or radar) a problem at 200m that it doesn't want to handle autonomously, it has only a few seconds to get you to put down your tablet/coffee and take the wheel. Mercedes and Audi[2] are currently (2014 models) handling this by making you keep your hands physically on the wheel.
>> "...the head spins at the thought of being legally responsible for a car you’re not actually in..."
If your house explodes in your absence because you left the oven on, it's your fault. My uneducated guess it that you might see legal indemnity enacted or a variation on some U.S. states' "no-fault" laws.
>> "... if we want our cars to drive themselves ... you will never be exceeding 100 kilometres an hour again."
I repeatedly encounter this argument against self-driving cars: they will obey the law. If you want the legal speed limit to be higher, raise the limit.
>> "Why then, if autonomous cars offer little unchaining from everyday driving, are automakers pushing them so hard?"
Automakers make what they think people will buy. They see lots of valuable man-hours spent driving, hours partially recoverable by companies and individuals if the car is self-driving. Governments are pushing it because millions of people are dying annually. (WHO predicts 3% of fatalities will be automotive in 2030.) U.S. seems to be playing catch-up; EuroNCAP has a roadmap to require more autonomous safety features over the next several years to get 5-star safety rating.
The 2014 Mercedes E- and S-klasses that I've tested also do active intervention if you try to change lanes towards a car in your blindspot. Via braking on the opposite side.
We (automotive active safety engineers) don't look at it as a percentage-of-inept-drivers, but more like the Trolley Problem[1], that is, overall harm vs benefit. To put it another way: seatbelts, airbags, and heart surgery hurt/kill some people, but the benefit outweights that harm.
EuroNCAP[1] requires increasing levels of automated pedestrian protection -- i.e. autonomous braking or avoidance -- to get a 5-star safety rating starting in about 2015. Because World Health Organization predicts 3% of fatalities in 2030 will be automotive collisions, and over half of those 3% will be pedestrian deaths[2].