Another argument in favor of "Good fences make good neighbors" is in international relations. For centuries countries have had borders that separate them from neighboring countries. These borders, patrolled by guards, have protected their inhabitants from invasions of various levels. (Centuries ago China built the Great Wall.)
While some fences are not good such as the wall constructed between East and West Germany and a border patrol of Russia that had guards shoot those who tred to enter, "good fences" have protected countries from drug smugglers and other criminal or dangerous elements from entering.
Clearly, statistics support the fact that the porous borders of the United States have allowed drugs and known criminals and unknown terrorists from entering this country. In a study from the Center for Immigration Studies it has been reported that
48 foreign-born militant Islamic terrorists have been charged, been convicted, plead guilty, or admitted to involvement in terrorism within the United States since 1993.
(These, of course, are the ones who have been recognized and caught.)
Even those who are not of a dangerous level who enter illegally are often a financial burden as they become part of an ever-growing welfare roll in this country. Illegal immigrants cost the U. S. $100 billion a year.
“Good fences make good neighbors” is still very relevant today in the areas of law and politics. This statement remains true because people are still very much liable to have conflicts when they come into contact with one another. Good fences (literally and metaphorically), reduce the number of opportunities for conflict.
For individuals and their neighbors, good fences of the literal sort are still important. They reduce the potential for the neighbors to come into conflict. For example, a good fence between my yard and my neighbor means that we will not argue because his dog defecated in my yard or because his young children trampled my flowers. We can remain as good neighbors more easily because our interests do not come into conflict with one another.
We also set up metaphorical fences to avoid conflict with one another. We have things like noise ordinances so that we will not make so much noise that we disturb other people around us and come into conflict with them. We make contracts with people to clearly delineate our responsibilities and their responsibilities so that everything will be clear and we will not have conflicts. In our world today, it is hard to avoid offending others and causing conflicts, so it is still relevant to have good “fences” so that we can remain on good terms with those around us.