Originally Posted by orbitmic

My first point, and I'll restate it again, is that once you enter the international section of most European airports, including CDG 2E, you cannot leave except by plane. There are plenty of reasons for that, including the fact that if you fly ATL-CDG-LHR, you will remain airside during your connection having bypassed the place where you can exit to immigration without ever entering Schengen territory. Once you want to leave the 2E departure area, you are therefore asking to enter the Schengen territory (in this case France) from a place which has no inbound passport control set up. This is both technically impossible and something that typically (and I'm not saying it is right or wrong, just that it is the case) attracts great suspicion on the part of immigration authorities because, just as though you were trying to cross a border away from border stations after passing one and ignoring it to continue your way, they will suspect the worst before considering more innocent explanations. In some airports, like LHR T5, there are hourly escorts for anyone who has entered the terminal by mistake but no such thing at CDG so quite literally, what staff have to do is call the police to escort people through doors that are not open to the public back to a place where they can be immigration cleared. It is neither convenient (it may take a while before people are available to escort you and they will not look at this with sympathy) nor easy (you are not in control), and it can even result in a more thorough immigration check than what a - presumably - US citizen just entering France for a holiday (let alone to merely take another flight from ORY!) could expect.