Will an identity system allow me to lie?
I (and I expect most others) often provide false data to sites asking me for personal data. I'm more likely to do so if the site is asking me for specific identity information as opposed to some range. For instance, if the site asks for my birth date (or even age) it's very unlikely that I'll give the actual date (unless it will eventually serve as some credential). If instead, the site provides me a set of ranges of ages from which I can select I am far more inclined to be truthful.
Now, if an SP were to ask an IDP of mine for my age rather than me directly, what happens if the SP and request are such that I don't want the IDP to provide the real value. Does the IDP provide a value from a persona I've set up just for such requests? What is the meaning of such an assertion if there is another persona with my real age, i.e. is the IDP asserting to the truth of its claim or merely to the fact that its asserting a value previously supplied by me?
Seems to me that the problem with the current status quo of sites asking for my age is that there is no 'fall-back' option, e.g. if I want to proceed with setting up the account or purchasing whatever, the HTML form requires me to provide a value for the field. There is no negotiation possible, no leeway in the site's identity demands and consequently I respond with the only option that satisfies both this demand and my desire for privacy - I lie.
In the brave new world of identity, perhaps there is no need to lie. If an SP asks my IDP for my age, the IDP might respond with 'Why do you need it?', to which the SP would say 'Demographic study', so that the IDP would finish with 'Well then his age range of '35-45' will be sufficient'. Because there needn't be a binary yes/no for release of identity data, but a negotiated middle-ground, its more likely that both the SPs and mine can be satisfied.