A border separates a country from the other in other words, it's the line or boundary separating one country from the other.
Actually with what am seeing, and what's currently trending now in my country (Nigeria) a lot of people are moving out of the country even without a opened border or free access to counties. I can count up to 10 people if not more that I know too well that has moved to the United kingdom in the last two years, the rate is on the increase over the years not decreasing. So making it a free access would make more people move out of the country in search for greener pasture.
Though opening up the border definitely has its advantages and disadvantages which I'll quickly discuss, join me as we dive into it:
Making the border a free access to everyone will help those that are into buying and selling of foreign goods, they buy goods from other countries to resell it in their various counties. The goods will even be cheaper as they won't be charged with any levy by the military personnels for importing or exporting goods in and out of the country.
Also just as have rightly mentioned, a lot of people that are experiencing hardship in their respective countries will migrate to another country where things are easy. Especially in my country (Nigeria) I know alot of people and including myself, smiles... that are ready to leave the country whenever an opportunity comes, so with this it's just a free ticket to achieve our dreams. I'll gladly utilize the opportunity to move to my choice of country and start a new life.
Moreover as good as opening the borders can be it also has its own disadvantages too, infact I think the disadvantages might be too much for any country at all to manage or comprehend.
First is the issue of crime that will be done if these opening of borders come to reality, a lot of people will commit crimes and get away with it'll be every easy to appear and disappear in any country of your choice free of charge, unlike now that you have to go through many process before they will grant you a visa.
There won't be proper monitoring and the society will be so disorganized, it will be hard for the country securities to watch over the people of a particular country, it will just be like a city or country with no law and where there's no law there's no sin. So it's just like saying everyone can do what they like anyhow and when they please to do it. The end result won't go well at all.
In addition, with people moving in and out of the country, these will make some countries less populated and some over populated. Countries that are suffering from recession, economic crisis, war and all sort will definitely be under populated, while the countries that has potentials will be flooded with various people across the globe. This will in turn make these countries suffer and make them hard to live in.
Above all, I don't see anything worthwhile in making the borders widely open for people to move in and out freely, due to the hazards behind it, I think it's best, very wise and safe to keep it secured how it's now.