[stavros]

I'm not sure that this would work, mainly because it would mean that all the documents would have the same hash, rendering the content ID system useless. I don't know how many bits a content I'd contains, though, but I imagine it's enough to avoid having too many collisions (as that would reduce the usefulness of the system).

[gorbypark]

Right. That is the OPs point, however (as far as I can tell). They think it will be intentionally abused by governments as a way of collecting data by mandating certain hashes that will intentionally have many collisions.