There's a great article on security issues at http://www.theatlantic.com/issues/2002/09/mann.htm
It talks about Bruce Schneier, a big expert in all types of security issues, including computer security and cryptography. At any rate, when you talk about a new security system, there are two questions to ask:
1. What problem is it trying to solve?
2. What happens when it fails?
Ok, so for the first question. Let me say this really quickly, identifying an individual is not a goal
. It doesn't achieve anything except for some psychologicaly comfort (which I hypothesize is a big factor involving ID cards.) It can not assess whether you like watching football games on the couch with a beer, you prefer barefoot walks on the beach, or you want to hijack an airliner to British Columbia. It does pretend to though, which is really bothersome to me.
I have no answer to what problem it's trying to solve. I think it solves nothing.
So when it fails, it probably doesn't fail in any particularly significant way. (I would say a failure would be trusting a traveler who ended up doing something that they were not expected to do. It can be said though that that trusted individual may have been caught otherwise had they not been trusted.)
We also hit this odd illogical element: If we have the system in place for 20 years, and no terrorist incidents happen, then people will say the system is a success and all americans should now have trusted traveler id cards. On the other hand, if the system fails, and a terrorist incident occurs, then the problem was not enough money/resources put into the current system, and we need to add more resources and get every american part of the system.
Either way, it doesn't really solve anything, and it's at a tremendous cost financially and to our freedoms.