>Having self-driving cars randomly stop short is a quick way to rack up a lot of "not legally at fault", but perhaps morally at-fault, accidents.

And I'm pretty sure, in most jurisdictions, slamming on the breaks unexpectedly and for no good reason, will get you at least a portion of the liability for an accident. The person who rear-ends you will get some too, but its not always true that you can't be at fault when you get rear-ended.

As you imply, no safety system should rely on others doing their job perfectly. That is an inherently unsafe system.