Migration is a very difficult and complex process and by not having a functioning concept to properly integrate migrants [short- mid- and longterm], states & migrants create parallel societies whose members are not able to identify with the country they're living in, resulting in frustration & a general feeling of alienation. This alienation very often leads to fear of the unknown, which leads to migrants alienate even further; it's a vicious circle from my experience. It's just like master Yoda said.
That`s a very good summary. It is also a fact that despite the oft said `humanitarian` reasons for allowing defacto immigration through asylum seeking for example as well as the established refugee intake methods, these processes are underpinned by economic policy. The traditional people of Europe and the British Isles, Republic of Ireland etc are not having children in what is considered economically sustainable numbers.
It is about demographics - governments want young populations in order to keep the consumption cycle going as well as providing the tax base for different societies. Those are key reasons why the negative side of having growing populations of people from countries historically and culturally very different tends to be more influential than it should.
There is also the element of same as it ever was regarding the attitude of the host culture. `They do not attempt to follow our traditional mores, their culture is too different from ours, their religion is an alien one that pledges allegiance to foreign powers instead of our rightful government and establishment - foreign powers that seek to overthrown our own order - and despite their often modest to poor financial circumstances they have an excessive number of children.`
Those kinds of opinions were expressed about the native Irish over a number of centuries including even the 20th.