It can also bring complications simply because of the people--it depends on how many, what their background is (especially relative to what the opportunities are in the target country), what support structures the target country has in place, etc. etc..

For example, I don't know where you live, but I can guarantee you that if you teleport everyone displaced by the fighting in Sudan to where you are, right now, the result would be an absolute disaster.

That fears are often exaggerated, used as an excuse to do nothing or be mean, etc., does not mean that immigration is universally without problem.