The fact that something can be used used in a dumb manner is good to know so you can avoid doing so, but that doesn't negate the fact that cars are safer overall with it than without it.
Seeing people abandoning the precautionary principle so they can latch onto an over-marketed, over-promised Muskian view of the future is sad. And in five or ten years we're all going to be looking back wondering what made us so dumb to think that computers could actually drive cars.
However, the inference that Autopilot reduces incidents per mile seems very likely to be true.
Though by the time you get to the 8 billionth mile the technology will have evolved, rendering the earlier data moot. So it will be pretty much impossible to do any sort of authoritative study on how safe this technology is until it is widespread, and mature.
You could have a car that never gets into little collisions that often happen to human drivers because of carelessness, but are rarely deadly, but the same AI might have a faulty reasoning every once in a while leading it to accelerate to 200kph before running straight into a wall. This hypothetical AI would have very few collisions, but maybe still be much more deadly than a human.
Humans are the only data we currently have significant numbers of miles logged for. Any extrapolation to AI is meaningless.
And the NHTSA doesn't count as a third party?
> I'm speculating that the reason for that 40% safety improvement is more a result of the difference between where autopilot can and cannot be used.
To say that tesla owners without autopilot tend to drive in situations with 40% more likelihood of accidents than those with autopilot, sounds like a massive stretch without data of your own.
Statistics is really tricky, even with very large samples at recent presidential election had shown that beyond any doubt.