If it’s RFID, there is no physical touch required. That’s the RF part. People have demonstrated (see http://www.schneier.com/blog/archives/2004/10/rfid_passports.html) that RFID tags can be read at distances of 20 meters. So, why is that bad?

Well, the most obvious question is one of safety. If I’m visiting Rome, for example - and I’m not picking on Rome, specifically, but it is known as a place where tourists should be careful - I would prefer that people cannot automatically identify me as a) a tourist and b) an *American* tourist. One can argue about how big the increased risk is, but there are certainly bad scenarios that this enables.

The curious question is “Why RFID?” There are good smart card technologies that require physical contact, which would seem to work great for passports, since you are in physical contact with customs officials when you use your passport. That the government has settled on RFID begs the question of what they need that RF portion for.

Cell phone tracking is a very different question. You wouldn’t use RFID to track people, you’d use it to find out which ones were Americans, and (depending on the information security), you could even find out more information about them.