Could airport biometric data really be used to make personalized synthetic porn?

It combines a real privacy concern with a lot of assumptions. A face image might be useful as a reference for generating a likeness, but having some biometric data does not mean an agency has a complete set of usable images, can freely combine them, or is doing this. The claim by itself is not evidence of a plan or practice.

“Facial images” and “body scans” are not one big interchangeable database. Airport identity checks and screening equipment can involve different systems, data, and retention rules, which may also vary by setting. A scanner image should not be assumed to be a detailed portrait suitable for making realistic intimate images.

If you want to assess a specific concern, look for the policy for the particular system and ask what it captures, whether images are retained, who can access them, and what uses are permitted. Without those details, the sweeping version of the claim is speculation.

There is a broader point worth taking seriously: biometric data can be sensitive, and misuse or poor safeguards would be a legitimate concern. But the jump from “an agency collects some identity data” to “it can produce pornography of every traveler” skips several steps. I would separate the general privacy risk from the unsupported accusation about what is happening.