There are suburbs of the city that are in German and French territory: Basel trams and buses will get to either side, with no notice you are crossing a national border.
You can cross the Rhine from Weil am Rhein (Germany) to Huningue (France) through a footbridge, with the only thing marking the cross being a German and French flags side by side, on the French side of the river.
https://en.radreisen.at/data/thumbs/_data_pic_Frankreich_Reg...
No border, no checks, even normal police nowhere to be seen. 75 years ago (and pretty much over the course of their history) these two countries were at bitter war between themselves.
I cannot fathom why people would do anything that could cause returning to those times a possibility.
As flawed the EU is, it has been instrumental in ensuring decades of peace. The (partial but undoubtful) loss of sovereignity for individual members should be considered a fair price to pay.
"Those who cannot remember the past are condemned to repeat it."