Because it is expected to be much slower to wait for police escort to escape from such a badly designed airport[*] than it is to go through the security screening to escape from the airport through the screened area.
[*]I.e. one where there is no way to leave the airport after exiting customs other than to go through the screened area. Unfortunately, such airports are common in the US.

Yup, SEA used to have this nonsense years ago at the S. satellite. I refused the search and the TSA drone threatened to call the police, to which I agreed. The airport cops (ptooey!) arrived, gave me the "security spiel" and some empty threats but in the end had no option but to escort me through the back door. Boy, were they pissed. Tee-hee ^

Let's see. No ticket to another flight. You are at your destination. All you want now is to get out of the airport, find some transportation, and leave. Amazing when all TSA would have to do would be to escort you out of the sterile area. Win-win for everyone concerned. Instead they bluster, threaten, and make a feeble attempt of intimidation through authority.

Congratulations on winning that one.

"Do you want to not fly today?"

Refusing a search does not constitute probable cause.

Your explanation makes perfect sense... but what I don't understand is why the airport is (still) laid out in this way. The rules about segregating passengers have existed for quite a few years now, and other airports have made the necessary alterations... why not KEF? It can't be that onerous to construct an extra passageway that would enable arriving passengers to exit the building without passing through the sterile area...

Don't quote me on this, but it might have something to do with the Duty Free stores at the airport. Icelandic passengers have a propensity to purchase huge quantities of Duty Free alchohol (since local prices tend to be prohibitively high) and the current layout permits pax to access the Duty Free stores upon arrival en route to baggage claim (which also has its own Duty Free store).

Also, the non-Schengen gates and the immigration checkpoint are located right at the end of the terminal - the furthest point away from baggage claim. Considering that no more than 5% of passengers are originating from a non-EU destination and terminating in KEF (versus transfering at KEF which would require a security check anyway or originating at an EU airport in which case Duty Free in sealed bags would be acceptable), there really isn't a significant constituency to justify it.

I'm sure you could refuse the search. But you would have to wait around for LEOs to come and escort you out of the airport. You also might have your record documented so that on future trips you would get SSSS treatment every time. Not worth it, IMHO!

What it sounds like to me.

Before 9/11� or even TWA 800, experienced this on UA FCO-MIL-IAD. The stop in Milan was supposed to be 20 minutes, barely long enough to load pax for the transatlantic leg. (No one then paid U.S. carrier prices just to go FCO-MIL.) Instead, we were told to exit the plane as rapidly as possible, bringing all carry-on with us. Exiting was not rapid, because some kind of LEOs were running all carry-ons through an x-ray set up in the jetway right outside the plane, clearly not its regular location. Two hours and a gate change later, we were back on the same 747�too many pax to tell if anyone was missing. Much speculation about bank robbers/jewel thieves/etc. but we never found out.

If there's a specific reason, and warrant or equivalent, to do this to catch a bad guy I have no objection. For random "because we can" snipe hunts, I do.

No legitimate reason exists to document your record as you are only following the rules as they exist. In addition, why should you even have to show ID to get out?

I disagree. It is always "worth it" to exercise one's rights, especially in the face of ludicrously stupid "security" policies.

No, didn't happen. Remain calm and polite, they would like nothing more than you to give them a resaon to escalate.

Opinions differ (obviously) on what is "worth it".

Until few years ago, Serbian customs at BEG used to the exactly the same thing - scanning all [checked and hand] luggage of all incoming passengers - to prevent any smuggling and avoidance of duty. Now they have red and green exits.

I flew in from CAI today at CDG and there was a passport control in the jetway. But I am not really sure what they were looking for, as I surely didn't have right to enter France [nor was I intending - only transiting to UK]

see also: FT: "Another visit to the USA...and another empty threat by the TSA", April 6, 2009

i always thoufght after Customs you just go through one way doors to the greeting area.