Well, for one thing, ID computers can selectively disclose information about their holder. For another, they can validate their interrogator. This gets around a big problem with cardboard identity cards: anyone can read them, and when they do read them, they read everything on them.
In my opinion, a 21st century ID card should exploit three key technologies—microcomputers, biometrics and digital signatures—to provide a service that citizens want, that makes life easier for them, that they will voluntarily choose to use. It would be even better if the card could provide a special service for citizens that they can’t get without it. Somewhat counter-intuitively, that special service may well be privacy.
The singular advantage of using computers, biometrics and digital signatures is that they can work together to disclose facts about someone without disclosing their full identity. Your ID card could, for example, send a message to a machine confirming that you are over 18 without disclosing who you are or what your citizen number is. The recipient of that message—a bar, say—would know that the digital signature from the ID card is real and that the message had not been forged and let you come in and buy a drink: but who you are could remain confidential.