It's like you refuse to comprehend what I've typed, the caution or the seat belt of my analogy would be a password.
You specifically cited the controller in that post I quoted, but okay.
Your analogy still doesn't hold because you don't have an active relationship with the car manufacturer when it comes to wearing a seatbelt or not, and the seat belt is protecting against loss of life. And more people know that wearing your seat belt is a good idea than password protect is almost necessary when dealing with online store.
So the stakes and contexts of the situations are completely different.
Furthermore, there is no default-on function when it comes to most cars. You always get into the car and chose to put on your seat belt, whether it's the law or not. With the default-on password protect, you have no choice but to have it in place or opt out.
And to your point of "how will people learn not to make mistakes," what will it matter if people can't make the mistake in the first place? Instead of assumptions of what people know, make sure they understand by forcing consumers to opt out of password protect.