Backlash
Trouble is, if autonomous cars are only, say, 99% safer than human drivers, what happens when a case is reported where one is responsible for killing someone?
There are lots of precedents for damaging backlashes. In the field of transport, just look at the completely different standards applied to rail deaths compared to road deaths. If the cost-per-death of the Hatfield disaster were applied to motorists, a year's insurance premium would cost more than a new car, and it seems statistically likely that the rail disruption that followed it caused more deaths (by driving people onto the roads) than the crash itself.