[fransje26]

That's because you have the right to travel freely between Schengen countries.

Asking for an ID or passport when embarking/disembarking would be similar to having an ID check at a border, and would therefore be a border control, i.e. no longer free travel.

Of course Schengen countries have the right to temporarily re-enable border checks.

[xeornet]

I imagine it's the same as a police officer asking for your name on the street. They are allowed to ask, and you are required to provide it. There's no restriction of freedom happening. I think it's logically prudent to know who is on a flight.

[bloomark]

You also have the right to travel freely within the domestic US.