Again, I'd highlight the lack of appreciable benefits as a very good reason as to why this is a very bad idea. Things like function creep also concern me, in that once the card is implemented it's nothing to decide that it should hold just a little more, and more, and more. Add to those the fact that the people who seem to think this is a brilliant idea seem to have a fairly limited understanding of the technology behind it, and it just sounds like a whole lot of trouble over nothing.
It also sounds very convenient having all the information about you you'll ever need stored on one card, but stopping and thinking about the consequences when something goes wrong (When, not if), suggests that it may be worth the extra trouble of carrying a few extra cards around for each function, rather than risking having all of it compromised in one blow.
Regarding the point that information is easily accessible anyway, I'd point out that it'll take a significant amount more time, and effort to attain criminal records, medical records, religious affiliation, employment history, credit background, and so on, from a range of individual institutions, than it would to read them all off a swiped card. Of course it's still possible if the person is dedicated, but why hand it all over to them in one go, on such a large scale?
In relation to securing the card itself, what's the plan team? PINs and passwords are fine for something relatively trivial such as a bank card, but what about a card with all your information on it? Would a four digit code really convince you that your information was safe? What are the alternatives? Biometrics would require huge amounts of infrastructure spending, and to be honest is often not really at a level where it's appropriate for securing information of this magnitude. I struggle to think of any form of security available for such cards which would put my mind at ease.
For anyone arguing that these cards would be secure, I'd advise reading about their implementation in other countries, where this has been demonstrated fairly clearly to not be the case, and in some cases where such cards have proven ridiculously easy to compromise.
If there were actually some tangible benefits for society as a whole through these cards, and reasonable attempts at assuring me of their security, fault tolerance and so on, then I may be a little more open minded about it, but I think for the forseeable future this is a bright idea we can do without.
Edit: On a sidenote, I'm going to be immensely annoyed if this comes to pass due to "terrorism concerns".