To throw my purely anecdotal/subjective evidence into the pot, my experience with Autopilot is that TACC is a huge safety win (not that you can trust it completely; you still have to pay close attention), but Autosteer is a convenience feature only which does not noticeably improve safety, and may on balance degrade it in the population overall. The only way Autosteer is going to be safer is when the driver somehow becomes incapacitated (heart attack, falls asleep, other loss of consciousness). In this case Autosteer will eventually notice that the driver is not putting force on the wheel (unless the driver happens to be slumped over on the wheel or using a defeat device) and bring the car to a stop. There's at least a chance it would do this before hitting something. The nags may also wake you up if you fall asleep, unless you fall asleep with your wrist hooked over the wheel for example.
On the flip side, I think Autosteer when misused (trusted too much) makes people less safe. It makes you more likely to fall asleep in the first place. It makes many drivers more likely to take their eyes off the road or their hands off the wheel for a variety of reasons. I think the fatalities we've seen fall into this category. Granted there is an element of misuse here, but face it, people are people.
So you have on the one hand some extremely unlikely scenarios where Autosteer might save you, and some very likely scenarios where people will misuse it and be less safe. Make of that what you will. Also note that ACC and AEB, which are without a doubt safety enhancers overall even with TACC's flaws, are also available in quite a lot of other makes of car by now, and the better versions of it are really just about as good as Tesla's (better in some ways, worse in others).
