I'm just trying to figure your posts out. Are you then making a case that there should be no identification required at the border? Somebody says they're a US citizen and you'd just take their word for it?
Absolutely not.
CBP has no authority to arbitrarily fingerprint and photograph US Citizens. As far as I know, no law enforcement agency does.
This was not about identifying who they were. That is done by checking names and DOB’s in the computer and verifying documents.
This was about keeping tabs on them.