He specifically said that about code in Emacs itself, and only insane people would disagree with that position when you can just change the original function.

He specifically said that about code in Emacs itself, and only insane people would disagree with that position when you can just change the original function. IMO, and I suspect RMS would agree: defadvice shouldn't be used in code you distribute to others, because multiple pieces of advice can conflict, and the code defining the advice doesn't control which advice is loaded first. It is still a valuable tool for usage in personal configuration and for prototyping.