Hadrian's wall, The Berlin Wall, and China's Great Wall did not work. People just went around or under them.
Hadrian's Wall: Actually effective... So effective that it was later followed by another Wall called Antonine's Wall that advanced the border even further North.
Berlin Wall: also very effective. Kept East and West Germany divided for decades, politically, economically, and socially... re-unification of the country could not really properly occur until after the Wall was torn down.
China's Great Wall: again very effective wall against the Mongol Hordes. Literally stopped so many raids from occurring.
The reason it's been absent from the commentary is that walls have, historically, been effective. The argument that people can simply go around walls is easily turned on its head. If people have to go around a wall, then you have controlled where they can go (proof that a wall stopped them from going literally anywhere they wanted to go).
The argument that walls are not effective because people can go around them is a very strange argument to see... because the whole point of having a wall is to force people to go around it! It's like arguing that cars aren't effective transportation because cars don't enable people to go anywhere they wouldn't already be able to go! (People can already walk to any location a car would be able to carry them).
