Because there are a number of encodings that are possible (7bit, 8bit,
quoted-printable, x-?, more in the future) if encryption isn't being
done and discussion of which one is appropriate for a given
unencrypted message is a huge can of worms.
...
You can choose quoted-printable for ENCRYPTED, but it is guaranteed
much less efficient and is always less safe. What's the point of
providing a stupid and useless choice?
As you have noted, what's wrong ith 8bit and possible alternatives
which may arise in the future?
As for "insure" versus "ensure", well, my Oxford English Dictionary
tells me "insure" is perfectly valid and actually a bit more precise
in this context.
Most style guides will agree that "insure" is the preferred term. :-)
-Ray