10 years ago, I was living in Europe and rarely, if ever, even got an entry stamp at FRA. You would slow down a bit as you hit immigration and just hold your passport up and were just waved through.

I think the issue the OP is concerned about isn't politics as much as the results of politics. There's also a basic faciliites design issue as well.

Most airports around the world have an entire section of a terminal or whole terminal(s) just for international flights. That's because in the vast majority of countries you go to, there is an exit program in place - you go through outbound immigration before going to your plane. Thus, there's a big part of the airport where, for all intents and purposes, passengers are in no-man's land. They are outside immigration, either arriving or departing. Thus, if you're flying from the US to a non-EU country in Europe or someplace in the Middle East or Africa, you can make a connection without having to deal with immigration/customs in the transfer country at all.

The US does not have an exiting immigration program. Thus, there is no section/terminal at the airports that are international-only, in the no-man's land. I know in the past you could transfer through - really popular for Europe-Latin America routings - but it was never a perfect system because you literally were corraled for the period of the layover. However, that's been done away with, to the detriment of the airlines. If you want to transit here - and I did so myself a couple of years ago, going from Mexico City to Sao Paulo and connecting in Miami - it's a pain in the .... If you're lucky you won't have to reclaim your luggage and recheck - this is dependent upon the procedures and "security" arraingments at your origin airport - but you still have to fill out US customs forms, stand in line, go through the entire entry procudure, having your carry-on luggage subject to secondary inspection, then you clear customs and have to stand in the TSA lines to get back through security to get to your departing gate.

I would not wish that on anyone, even if they have a visa or are from a visa waiver country. Entering the US is a hassle - I've had close to 100 international trips and while I've only been secondaried at Customs once, you never know when it will happen. BICE agents are sometimes very rude, the "helpers" yelling at you in lines, etc. I don't quite dread it - Dulles is excellent for me and I've never had a problem there but Miami and New York are totally different subjects!

If you're only here for a couple of hours, just to make a plane connection, it is a major hassle to go through and I think it should be avoided. Connect through Toronto or Mexico City or somewhere else.

And to the people who threw darts at the OP - I don't think you quite understood his point. His main point was not to visit the US for business/pleasure, just to transit through to get from one country to the next. Even I, a US citizen, will avoid that hassle.