Also, this assumes the checks are actually performed - which is a compute intensive operation for a human (names in various languages, etc). I once accidentally swapped passports with my wife, and we both boarded without questions. We dont share last names, and, of course, dont look much alike. Its bad security to rely on tired people doing annoying repeatable tasks where the risk of something going wrong is so low.

It is worth in the rest of the world. And besides, I've been there and it's not 2x. Everyone has their ID ready and it just takes a glance to check.

Worth it how?

On international flights, if an airline transports somebody who is rejected by the destination for not having the proper visas etc, they are heavily fined. So airlines are strongly incentivized to triple-check passengers and their documentation.

That's not a concern with a domestic US flight. If that's the reason why checking ID's is 'worth it', then it's not worth it.

Worth it as in there's literally no cost to doing it and it prevents unidentified people from boarding.

As funny as I find the anecdote, I would prefer any airline knowing who's on my plane. Wouldn't you?

Not really, no, it's just one more thing to go wrong and for me to have to dig out of my pockets. I'm happy for things to move along more efficiently, airplane processes are slow and annoying enough as it is. I don't care if some other guy got on the wrong flight, intentionally or not. That's his business.

How do you get 2x? I'd say you slow down boarding by something between 0.00x% and 0.0y%, since it takes an extra couple of seconds to do that, at least with the German system.

I'm intrigued about the system you are envisioning that creates the extra 100% delay.

It's not like the plane is going to leave earlier if the queue is processed faster.

Experience says otherwise; I routinely take use domestic flights that leave the gate early and take off early because they finished boarding early.

Maybe so, but that has nothing to do with the gate check-in.

The bottleneck is at boarding the plane and seating. Passengers stand in line on the jetway after they check in at the gate. The only reason gatecheck is rushed is to reduce amount of staff-time required at the airport. It doesn't get the plane boarded more quickly.

In Turkey, they are explicitly disallowed to do so, and has been the case even before 9/11, due to how Turkish transport licensure system works.

I don't think the watchlists really do anything. Checking your ID against the boarding pass is just yield management for the airlines. (Compare the cost of a full fare economy ticket 45 minutes before the flight to what some desperate person would sell it to you for, knowing that they either use it or lose it.)

How did the person on a terrorist watch-list make it through security in the first place, and why wouldn't that work for the actual boarding?

They check id and boarding pass at security before entering the terminal.

The don't actually check boarding passes at security in the US in my recent experience. Though your ID may be tied to your ticket in the computer system in some manner.