In the past a passport was sufficient on both ends, as far as I understand it. Now Canadians will have to do this same thing.
Given a world where they would have had to back down on US/Canada, it would have been a diplomatic disaster to go through and try to justify why they are not going to back down with the other countries.
But only when flying commercial.
And at each point the volume of hostile tone from US homeland security guards has increased. It can be quite stressful crossing at times and I generally avoid it, even though I'm only 45 minutes from the border.
It’s technically the US that requires Americans to have a US passport to re-enter USA. Not sure what they do, can’t refuse a US citizen entry into USA but I guess they could give you a hard time.
Airlines of course would imply have returned to board me without it.
Luckily I recovered it (bless you, friendly helpful people at the Sioux Falls airport) before my return flight.
(Replacing it would have had me stuck there for many days and requiring me to travel to Minneapolis or Chicago and beg for mercy at the consulate.)
The US, given its popularity as a destination, believes that people will deal with it. It has always been like that, traveling to the US from anywhere is generally annoying. Not sure how American tourists will feel about this friction, even if fair in theory.
We are allies -- but it is not a symmetric alliance.
You used to have to fill out in writing if you'd ever been affiliated to a communist party or done, drugs, where are you staying, how long, and be interrogated. I almost got deported a couple of times for saying I hadn't figured which hotel or how long I was staying.