The boarding pass combined with passport confirm a) name, b) that you're supposed to be on the flight, and c) that it's really you.
You are ignoring one detail: at the point you get on the plane all you show is a boarding pass. You could easily hand your boarding pass to someone else and they got on the plane instead of you. Like, if your brother-in-law is a known criminal fleeing prosecution who bought a ticket for a local trip, and you give him your boarding pass so he can board your international flight to someplace with no extradition treaty with the US.
I'm not ignoring any details. I know that my id and boarding pass are both scanned/reviewed at the checkin point. When that id is scanned, it can be in their system and displayed at the gate when the boarding pass is scanned.
So there's a 1% chance it will let the wrong person on the plane. And for the 1% where it stops the right person, they show their boarding pass and passport and the problem is resolved.
who says it's going to stop the wrong person?
Oh My God! The Airline Will Have Your Picture FOREVER! How scary is that?
They have no business holding on to the picture, or any other data, honestly.
no need to keep it past the point when the plane lands.
You can't have it both ways. Either it is BAD BAD HORRIFIC that an airline would take a picture of you while boarding the plane because they can keep it forever and use it for bad, evil things, or it is good that they take your picture when you check in because they'll obviously not keep the picture for more than a few hours. Which is it?
It is "fine" for them to use a picture and keep it for a limited (as in days at most) time for purposes of identification. I'm not sure what I'm trying to "have both ways" there. The problem almost anyone has with data collection has always been data retention policies and the mining of long-term collected data for behaviors, trends, and habits.