It is fundamentally diferent because it tries to judge your intent. Thus being both opaque and unpredictable. Car refusing to drive onto person is easily understood. Autonomous car refusing to drive you to corner of Baker's street because that is suspicious destination, with no recourse or explanation, is totally different thing.

This is why you can't leave judgment to technology, and why we have law enforcement and courts

"Plow into this crowd of people" is nominally wrong, but what if its actually "plow into this crowd of people that are hurting and robbing a family with two small children"

Your smart hammer refuses to let you smash into a glass window, but what if you were smashing into the glass window to save a child stuck in a fire?