What are the concerns using an RFID's unique ID as a security feature with NFC

What are the concerns using an RFID's unique ID as a security feature with
NFC

Came across a 2012 post Prevent copying nfc chip signal that advises:
"Recommend against using the tag's unique ID as a security feature."
What are the pitfalls of using the ID?



My application is to use an RFID transponder's 8-byte fixed unique ID to
derive a MAC or digital signature to authenticate the attached product.
Known or perceived shortcomings would be appreciated.