Scoping is certainly used successfully as an argument at the WG level,
through the more common pronnouncement "....that would require a change
to the charter.." Scoping aids WGs in being able to move the ball
forward in the direction of predfined goals, and hence is a process aid.
This is scoping at a micro level. I would think that the role of mission
is to provide scoping at a macro level, the kind of scoping that
determines whether a WG is established in the first place or not.
More importantly I would suggest, the simple requirement for making
binary decisions about whether something is in scope or not is necessary
but not sufficient. An institution surely needs some way to guide its
priorities as well. So one could for example agree with Eric's
definition of what the IETF's mission is, but once that is done, what
then guides the priorities of the IETF? I think you will find this to be
at the heart of the debate:
scoping=>smaller workload=>focused differentiation in the standards
marketplace+better quality output.
Every entity must decide what it is going to do uniquly better than any
other entity. This is the purpose of mission. Generic catchall missions
do not help entities keep the eye on that particular ball.