Well, it's a complex issue. Realistically, there are really only so many migrants a nation can take on without completely collapsing the economy; if you have facilities that can handle, say, 500,000 immigrants, and provide them with food, water, housing, clothing, and some sort of employment, that's one thing. But when you have five million show up, what then?
Furthermore, it's like the article mentioned: some of these migrants come into a country like Italy (especially young women), and they find no support structure; ergo, they end up forced into prostitution to survive. How is that beneficial? The politicians could do something about it, I suppose, but they're too busy protecting the status quo.
Just opening your border and allowing people to flow in is a fine concept, I guess, but in a lot of ways, it ends up causing more problems than it solves. Of course, if nothing is done, then eventually dams break and you end up with something like Europe in the 4th century, and hordes of foreigners pour across border, and the established nations that provided for limited numbers of migrants cease to exist.