Our current international regime of widespread passports, residency permits, visas, and border checks is barely 100 years old. Even in my lifetime (pre-9/11) the US-Canada border was a passport-free affair: just show the border guard your drivers' license (if you were the driver) and tell them you had nothing to declare -- they knew you were lying but didn't care.
It is not an iron law that international borders have to be dystopian "papers please" civil-liberties-optional free-fire zones. There is little point in the US policing either land border at all, but hassling NAFTA citizens (aka Canadians and Mexicans) traveling on business is especially absurd. A Schengen-style regime in North America (it's only THREE countries, should be pretty easy!) is way beyond overdue, but it seems like we're instead headed in the opposite direction as fast as we possibly can.
Open borders are the default state of the world. Anything interfering with our ability to travel should be in response to a specific, real problem. Instead, we've handed the door keys to our whole country to a handful of cops and private contractors who get paid more when they hassle us more.