It's pretty simple, really. Europeans don't work and retire early. The European welfare states need people paying into the system in order to keep their scam going, thus they brought in people from the third world hoping they would assimilate and pay into the system. However, these people don't assimilate and take more out of the system than they put in.
That makes the most sense too. Lots of people claim Jews are behind it, but I don't think so. There are tons of mainstream news articles by Jews pushing third world immigration, and multiculturalism for Europe (not sure why) . I've seen several articles (not as many) by Jews that encourage Israel to embrace Immigrants from Africa too though.
Do comments like this back up what you're saying, about supporting the system:
"Israel has not yet learned how to be multicultural. Israel is not going to be the monolithic society that it once was in the last century. Africans are going to be at the center of that. It’s a huge transformation for Israel to make. It is now going into a multicultural mode, and
Africans will be resented because of their leading role. But without that leading role, and without that transformation, Israel will not survive."
I don't know what else they could mean, claiming these countries won't survive without third world immigration?
Liberalism run amok?