A thought about ID cards

Here's a scenario that came to my mind last night. Let's suppose that ID Cards are introuduced, and after the years of problems of implementing them (including removing EDS/Capita/Serco/Crazy Bob's ID Services from the running of them at a cost of billions) they're now fully functional.

Now, suppose I'm in a situation where someone requires to see my ID Card to prove my identity for something or other. What happens if, before I show him my card, I demand to see his card so he can prove he is who he says he is and has the right to ask me to see my card? Of course, assuming he chooses to show me his card, then I'll have to ask him to accompany me to the nearest police station (or other nearby approved biometric data testing station) to be sure his card is a real one and not a forgery. But, of course, how do I know I can trust the data given me by the approved biometric data testing system? And so on, and so forth...

But, if we can't be trusted to be who we say we are, why should we trust that anyone or anything else is who they say they are? And thus do all political questions become existential philosophy.