All borders should be closed. There should be no mingling of countries ever again. We have an internet now so there is no reason to ever travel to another country. It is much safer to live on your couch and avoid any danger. I can watch culture on the television
If Europe closes it's borders to avoid it's putting more and more borders on the European Union thus making it less of a union. Separation of people usually makes them more nationalistic and even less likely to co-operative with other nations. The power to close the borders is a symbolic power of separation from unity. A solution to this problem is the European Union calling for huge humanitarian efforts from the countries forcing them to unite to financially help the immigration crisis or to invest in the raids of Isis or something to help. Humans and nations alike can unite or Seperated in times of crisis like the Axis separating from peaceful circumstances during the great depression and going to war with other countries and the Allies uniting to defend humanity from facism.
When countries close their borders to immigrants, it creates nothing more than a society where each country becomes more dependent upon itself. Our world will only be successful if each country can accept every other country. By telling a country "no, we won't accept your citizens who are in need," we are showing our stubbornness and will only create more animosity between the countries.
The real terrorists want other countries to close the borders. That way even more people will turn against these countries and be more likely to join the ranks of the terrorists. We also show the terrorists that we are afraid of them, and they want us to be afraid of them.
The problem is people who have decided to hate an entire group of people instead of focusing on who is causing the real harm. Much of the hatred is within our own borders, and closing them won't do anything to alleviate the problem. We would be teaching love, not building walls and shutting other people out.