The definition of a country is its collective identity, its character, and the place where this differentiates it from its neighbours is at the border. A country with lots of character but no border is not a country.
Like Brittany. It has its own language, its own version of Catholicism, its own history, its own climate, its own diet, its own customs. But its actually now just a province or a region or a Departement in France. Like Anjou or Languedoc or Picardy or a dozen others.
The border is something which serves to define a country. The effectiveness of border controls serves to define the effectiveness of a government. If they can’t get that right, what good are they?