I agree that the short and commonly used numbers that are often considered to be proof of ID are no longer suitable. When a computer can easily guess every possible combination of numbers in a set in seconds, it's not really sensible to use it for validation.

However, even if we all had a unique 4096 bit private key with which we identified ourselves, it would still essentially be a number and it would certainly be able to be stolen. Stealing a number is more or less the same as stealing a private key or stealing a classified electronic document - it's the unauthorised access and copying of information. Society has broadly come to accept that this is considered stealing.