It's not as simple as "just make sure it works on everyone". Even if it were physically possible to capture the face of all 7 billion people on Earth, you'd start running into issues of false positives/negatives, overfitting, etc., and furthermore it would basically require every person to be periodically scanned from birth until death to ensure that the algorithm can recognize new faces.

This is a different objection than the original objection. (effective accuracy vs specific bias).

With a pervasive system, unless people are hermits, they’ll get scanned periodically, and with other bits of information the changed face can be correlated with the same person (I go into a salon looking one way, come out different, go into a boxing match, come out different, but I’m following my routine and go to the same subway stop and convenience store and use the same payment method, etc.)

And then you just have a different implementation of China's social credit surveillance system...

there are of course examples of technologies that do not work for their stated purpose, but I think in general technologies do work pretty much for their stated purposes if people can use the technology correctly.

Generally the arguments against a technology is not that the technology does not work for its purpose, but that the way humans will use it is problematic.