I'm against them - they would likely not work (unless it's the unsaid desire of open-borders advocates to change irrevocably the nature of their country/society).
Borders didn't arise artificially, they arose organically.
The Great Wall of China was a border, still visible from space, built to keep out foreign armies and people.
Hadrian's Wall in Britain was also built as a border to keep outsiders out.
And humans aren't the only species of animal which has borders - just search on youtube for wolves, leopards, hyenas, etc., defending their territories along their borders from invasions by conspecifics.