Ten years ago, we opened our building's front door with a badge. Five years ago we paid public transports with an RFID card. Today we pay for our bread with the same system and tomorrow we would probably be able to authenticate ourselves with something similar.
Basically, an NFC tag is only a physical support, just as a DVD is. It is easy to imagine how it can be protected against malicious alteration or prevented from being read (i.e. understood) by an unauthorized third party.
However, to prevent it from being cloned as-is (even if encrypted) seems impossible to me.
What prevents me from creating kind of an ISO image of the NFC credit card of my customers, writing it on a blank tag and then using it to buy my cigs?