I did this during an international trip last year coming back into the country. The guy mostly seemed confused and kind of suspicious, but it was nbd.

They will potentially take you out of line to a side room to hand you off to someone else. It seemed to be an area where they deal with any oddball kind of things. There was a lady ahead of me who was more raucus and upset about some issue with her ID. The guy who checked mine mainly seemed kind of bemused, like it was unusual.

Be prepared for “We have the biometric data from your photo already, why do you care?”

You’re not obligated to give them a super detailed justification. Just remain polite and unconfrontational, and explain that you prefer not use the system as long as the right remains afforded to you to opt out.