The problem with making something foolproof... as the saying goes.
I would say that the number one problem with automobiles as they are sold today is the drivers themselves. People who understand how their vehicles can and do function are a rare breed. Essentially, auto manufacturers must cater to the lowest common denominator, so yes, completely unpowered braking is off the bargaining table.
I've noticed this most in the EV DIY sector, where people create workarounds for problems that simply don't exist in the ICE world. Some are safe, some are unsafe, some are genius. BUT, what you also end up with are vehicles that might be difficult or impossible for the general public to operate properly. And that is always a dangerous situation.
Just like the old joke about the retired couple who got into an accident and wrecked their brand new motor home. When the CHP arrived on scene and asked the old man who was driving what happened, he responded: "I have no idea, sir. I was driving along and started to feel tired. So I turned on the cruise control and went back to make a pot of coffee."
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