Leaving the USA at SFO, I tested out "Opting out of facial recognition scans before boarding" procedure to see if it indeed exists and will be followed.
It didn't go very well.
The gate agent argued saying I couldn't opt out. I insisted that I'm allowed to, and they pointed to a sign on the wall explaining the "Biometric verification privacy policy". The sign says "Customers wishing to opt out may speak to a gate agent or CBP officer for a manual verification" clearly at the bottom.
The agent then told me I have to opt-out *in advance with CBP*. I pointed out that the sign says "or gate agent" and asked if she was a gate agent. She insisted again that I can't opt-out but by that point another agent heard the discussion, came over, and showed the first agent how to place my passport on the scanner and sent me through. I overheard her telling the first agent as I walked away, "If it's a US passport, it's OK."
A flight of probably 300 people, I'm definitely the only one who opted-out today and by the gate agent's confusion, I suspect I'm the only one who has opted out in a long time.
I'm in every system there is (and China already has my entire SF-86) so it's not that I'm some off-the-grid paranoid who doesn't want to be in "the system" - but for privacy rights to exist at all, it's important to use them when you don't need to and keep them available for people who DO need privacy.