Another reason I don't like it is that, as presented, anyone can set and inspect any attribute. That includes typoed attributes, or just someone being "nasty".

Isn't this pretty much always true? Besides, I did mention that validation was a necessary part of implementing this concept: validation could easily include "you are(?:n't) allowed to modify this value".

And I fail to see the benefit for the user of this class. To me, the only advantage I can see is that the author of the module saves adding a few accessors - at the expensive of an inflexible, complicated, do-it-all routine.

Could you please expand on this? I guess I don't understand what is inflexible or complicated about the approach -- it seems simpler and more flexible from my (admittedly inexperienced) POV. Clearly, I'm missing something, and I'd like to better understand what it is.