The GP seems to be describing "auto hold", which is a different feature from hill start assist, and is newer and less prevalent.
There have been many deaths over the years where drivers forgot to engage the park brake, then stepped out and got run over by their own vehicle. Including, sadly, Star Trek actor Anton Yelchin. If his car had had Auto Hold then he would very likely still be alive today.
The only scenario where this could have a negative effect on safety is where you, the driver, were used to driving a car with the feature but got surprised by its absence when driving an old car. But as I facetiously illustrated in the post above, this is not a valid argument against new safety features. Any accidents that this scenario might cause are far outweighed by all the ones that will be prevented in the long run.
Anton Yelchin's death was more annoying, it was a design defect that pushing the gear lever all the way to the top didn't put it into P (like cars of the 80s, of even 50s), the gear lever acted more like a 4-way button, and drivers needed to push it twice (or 3x?) to go to park. Unfortunately his car was probably not new enough to have auto-park when driver door is open. His family got a settlement from the manufacturer..
Which to be clear is all I did myself, but I did say it that way honestly. "there is no way that..." doesn't pretend to supply any proof, just the reasoning.
Neither of your attempted counter-examples actually amounts to the same sort of reasoning.
Except in a way you are also right and that rightness actually supports my point. I would equate you seatbelt nonsense with bicycle helmets, where it is quite up for grabs if they have been a net positive, because both the riders and the drivers are falsely trained to think the cyclists are safer and don't need to worry as much. There are not many real studies, and the few that exist, you can make them say whichever side your emotional belief wants.
But I wasn't quite going there. Operating a vehicle is operating a vehicle. Until such time as the driver, or rather mere user, bears absolutely no responsibility, like riding the bus or a train , or maybe an elevator, then "there is no way" yes a simple assertion, that it's good to train everyone that they are riding in elevators where they only need to maybe press one button to say what they want but beyond that it's out of their control and so out of their responsibility what happens after that, because we do not actually live in that world yet.