I think it comes down to this:
If OPES is building a standard interface which allows a content-provider
a lot of flexibility in implementing *its own services*, and/or allows a user
a lot of flexibility in adapting content to his own needs, that's
probably a good thing.
If on the other hand OPES is building an interface which allows a third
party to modify content that is obtained from other information providers,
I don't see any way that IETF should support it. Even requiring consent is
not enough if the user or provider can be coerced into providing that consent.
When OPES proponents gloss over the difference between these it doesn't
give me confidence that they can be trusted to develop appropriate protocol
mechanisms to deter abuse, much less recommend policy for the use of OPES.