I have a question: why do European countries ( and others) have a passport control step before departing the country and the US does not? To clarify, we left Iceland a few days ago. Upon departure, after checking in, dropping bags, and going through security, we had to pass through a departure immigration step in which an officer in a booth scanned our passports. What is the purpose of this step? To keep "baddies" from leaving the country? To track who is in/out of the country? Something else?

The US does not have this final step incorporated into the physical airport space. Why not? Is this because the US airlines and/or TSA are performing some kind of verification upstream instead? Or the US just doesn't do it? Or something else I'm missing?

This question sparked a big family debate while waiting in the airport lines, with teenagers positing all kinds of wild theories. I said I would submit it to Flyer Talk, knowing someone here will know why the procedures are different!