SOmetimes, I'm in a cab and the driver's confused about directions, and I HAVE TO SWITCH TO FRENCH! THE HORROR!
Seriously, we could let them all in and they'd barely be noticed.
And let's not delude ourselves: the giant social welfare states in Europe and the United States act as magnets for refugees and immigrants.
The level of cynicism in the world's leaders is breathtaking. How many leaders said anything along the lines of, "We will take as many refugees as our people are willing to feed, house, and clothe, since the people of this nation are the most generous, loving people on earth"? Not a single one. It's always got to be the job of the State when a politician comes up with an idea. And of course the people get to pay for it through coercive taxation no matter if it's a good idea or not ;-)
Putting that aside, this would be happening in some form without that, because of climate change. The sad fact is that we're entering a period of increasing global instability, as previously livable regions become unlivable, and visa versa. I can't think of a single reason why some desperate Eritrean (for example) would say to themselves, "Oh no, these people who have been central to that process of climate change don't want me to live with them. I guess I'll just stay here and try to make it work. Maybe I'll starve and die, but hey, it's the law."
Zugzwang.
Nice? No. But what's the alternative, committing state-level suicide? That's why the first rule of rescue is ensuring the safety of the rescuer: if the rescuer is down, there's no hope left for the victim. And if Europe goes down, that will not help any migrants, either.
Any concerns regarding massive immigration, cultural differences, homeland security, etc. are labelled as xenophobic hate-mongering, despite plenty of evidence to the contrary.