For those of you who travel in the united states, you'll know they now have facial recognition scans when checking your id. You can opt out by telling them you don't want to take the picture. I do every time, but I wonder what the point of the scan is if you can just opt out. That given, why do you think they do it? What prevents them from forcing you to do it?
To those of you who live outside of the united states, have you seen a similar increase in security at your airports?
Palantir, which the US gov is now (let's not kid ourselves, has been for some time illegally) contracting, probably already has your face either from street cams, security cams in various company buildings, or from social media at this point, so letting you 'opt out' is probably just theatre to avoid angering people at airports.
There is little point in refusing it. The biometrics are already in the database - the scan uses them to let you in without using your passport. Refusing to use the system will not take your data out of the database.
Domestic flights within the united states still require an id. They recently (in may iirc) require you use a "real id". I guess those are harder to conterfeit, but still they strengthened the traditional id requirement recently, so I expect that to remain the standard, at least for a while
Why: Think of this as a trial working towards full automation. They aren't there yet and are not probably legally allowed to do so, but the idea is that you can be fully tracked like the British, Chinese, and other biometric adopted countries.
Prevention: Reliability and legality. As I mentioned I don't think they can force it in the US for travel yet as it's not legally allowed, nor is biometrics entirely reliable as is apparent when facial recognition fails.