Do the very nature of illegal immigration, as in undocumented, there are fewer safeguards to protect individuals in the host country. Criminal aliens can simply leave the country, start a new identity in another Shengen area country by claiming refugee status. Legal immigration can help prevent such scenarios from taking place.
Those in a nation illegally are breaking the law with every breathe they take. Most nations make it extremely difficult to enter illegally, with the immediate arrest and deportation of non-residents without legal reason to be there. It is perfectly understandable for these policies to be in place; statistically, crime rates among illegals are greater than those citizens rightfully in the country.
Hundreds of people have died in Europe this year as a result of terrorism. There have been people who have been run over by vehicles while they are trying to enjoy a Christmas market or a holiday. Italy has to do something in order to protect its citizens. This is a start.
Many people just assume that all illegal immigrants are in this country because they are criminals looking for an easy life. This is most often not the case. Many peope come here to flee the dangers of their home country. Others are here illegally because they were brought here as small children. Some illegal immigrants have never actually known their "home land." We need to be careful when deporting these people, and take careful consideration into the circumstances of each case.
With the recent terrorist attacks in Europe, countries such as Italy are looking for ways to prevent future attacks. Unfortunately, mass deportation and zero tolerance of illegal immigration are ways many countries are relying on to help prevent terrorism on their soil. There seem to very few other options to successfully combat terrorism at home.