From where I sit, it seems as if there are various rights and perks available to many of us, from being allowed to operate a vehicle, park said vehicle in a designated location, through obtaining health care, ending up with simply being able to identify your corpse at the end. You don't have to carry an ID relating to any of these abilities or entitlements, but you run the risk of being denied something something to which you *are* entitled, if you don't have some proof of this entitlement.

In the US, job applicants must show two IDs proving US citizenship or some other accomodation in order to start this job. This is mandated in a fairly recent law that aims to reduce the number of illegal immigrants working in US jobs by curtailing their access to work in the US. At my job helping to run a small convenience store, I routinely check IDs to insure that people desiring to purchase tobacco or alcohol are old enough to legally buy these controlled substances. My driving license has my blood type and instructions that I am an organ doner should I be unable to represent myself in these situations. While I don't really think that someone might mistake me for someone under the age of majority or unable to drive, I really think that there might be times when having a health care provider know what sort of blood to pump into me, should the occasion merit this action without having to wait until some of my remaining blood      is typed and cross matched. Not so long ago a young girl died after heart surgery when no one checked her blood type before transplanting an incompatible heart from a donor of different blood type.   

Dave