Without cell walls, with open border cells, cells would fall apart and cease to exist. Cell membranes hold cells together and prevent invading organisms from destroying the cell. What is true at the microbiological level, is also true at the macro-sociological level.
Frontex, the European Border and coast Guard Agency, has reports that there has been an overwhelmingly significant drop in illegal immigration in countries which have constructed walls, and strong border defences: http://reliefweb.int/report/world/frontex-annual-risk-analysis-2017.
ungary, for example, which had a strong border defence, cut illegal immigration from Serbia from 200,000 to 25,000. This makes nonsense of cosmopolitanist U2 front-man Bono’s claim that there is no wall high enough to keep out the terrorists: https://www.blabber.buzz/politics/conservative/102180-bono-to-world-leaders-no-wall-high-enough-to-keep-out-islamic-terror. Plain wrong.
Walls have been built by countries for thousands of years – the Great Wall of China, Hadrian’s Wall – and although in themselves have not been the sole mechanism of defence, have at least established boundaries and no-go zones. It has meant that the people are serious about what is their land, just as a fence between you and your neighbours says the same thing.
Let a thousand walls flourish!