Here's what I mean. Imagine this situation:
You're pulling into your driveway in your self-driving car, and one of your kids left a lawn gnome there, blocking it. The car won't go forward because there's an obstacle.
Simultaneously, a driver looking at their phone and not paying attention comes careening down the road. They're clearly going to rear-end you, hard. You COULD just pull forward and out of the way.....but the car won't, because of the lawn gnome. It can't know the lawn gnome doesn't matter in comparison to the damage your car is about to suffer.
Imagine this flip scenario:
You're pulling into your driveway in your self-driving car, and one of your kids, a toddler, is in your way. The car won't go forward because there's an obstacle. Otherwise, same situation as above. Now, you ABSOLUTELY do NOT want to pull forward, because you'd rather get rear-ended than run over your child.
Even if you want to nitpick this exact scenario, surely you can think of a hundred similar contexts yourself, where driving involves understanding the value of different pieces of the car's immediate environment. A car cannot know the value of a child versus a lawn gnome, nor can it reliably detect the difference.
Even if such a situation only arises once in a thousand days of driving, with hundreds of millions of people on the road everyday, that's thousands of times per day. That's really bad.
Is it statistically better than the amount of harm done by human drivers? Possibly. But we all still get in cars believing we'll be better than other drivers. Who's going to get in a car when any given car has an equivalent chance of making a bad decision all on its own? It's just like getting in a car with a drunk driver.
Who's going to sign up for that? Not me, that's for sure.