One plausible alternative is that we don't deploy systems like this, which have the ability to cause widespread damage including loss of life in moments, until we have worked out how to secure them properly against a single point of catastrophic failure like that. There are things that could be done to mitigate that threat in the meantime.

This is set against the knowledge that existing human-driven vehicles are involved in many tragic accidents per year, also causing widespread damage including loss of life. But there are other things that can be done to limit the damage there as well, without relying on autonomous vehicles as a silver bullet.