I too can take an arbitrary parable and make it fit any occasion.
For example, I could apply the same (lack of) reasoning you did and
demonstrate that trying to enforce the restriction on nested cte's is akin
to calling a sheep's tail a fifth leg.
However, I don't see how doing this helps us to reach closure. So,
instead of engaging in the usual invectives, let's try to stick to the
The bottom line is that one can make reasonable arguments for either
position. You don't like nested cte's because they neutralize many of
the benefits of the split-UA model. On the other hand, if I tell a PEM
UA to send a message with full privacy, then I do not want someone
figuring out what the structure of the contained object.
Again, I stress that these ar both reasonable positions. The only
solution therefore is a conformance statement indicating that a PEM+MIME
UA must give the user an option as to way to proceed. The market will
then sort this out pretty damn pronto.