> As a library writer, I'm free to change or remove anything that starts with an underscore because, if someone else is depending on it, frankly, they had it coming. I can assume everyone who uses my library is a responsible adult and I can treat them as that.

Totally agree, as an user, I feel anxious whenever I have to use underscored names. It's great that Python still allows me to do it and there were few times when it was useful, but when it stops working I know it's 100% on me.