European countries are working hard do vet people and still make sure that refugees have a safe and stable place to live. Unfortunately there is no real litmis test for who might or might not be a terrorist. Hate comes from all walks of life and the person who might be your terrorist is someone else' martyr.
Europe contains many different countries with different governments and policies. One country can border several others and there is not enough communication between the countries over border patrol. One person could easily go from Belgium to Germany, pass through several countries during their travels and never be stopped. There need to be stricter guidelines on regulations on travelers.
European countries are not doing enough to stop potential terrorists from immigrating to the continent. The European Union must do more to screen all Middle Eastern refugees, as well as set up more restrictions regarding movement within the Euro-zone. Furthermore, European countries need to invest more into security and military resources that can defeat terrorism.
It seems that every day there is a new headline about a terrorist attack happening somewhere in Europe. This is an indication that European governments are not strict enough about security measures that will prevent terrorists from sneaking past their borders. The standard "open door" policy unfortunately allows terrorists to enter Europe way too easily.