It must be nice to be able to ignorantly blame minorities for all your problems, without explaining why.
You might be interested in knowing that, at the very least, Sweden (can't talk about the other Nordic countries) is far from homogenous (but who needs facts when you have stereotypes?), having seen significant immigration from the middle east, Asia, eastern Europe, former Yugoslavia and more, and has, as a percentage of its population, more foreign-born residents than the US, yet manages to maintain this economical model.
The comment on the 'lack of social problems' is funny too, as, though immigrants are overrepresented among criminals, proper welfare services probably do a lot more to reduce crime than having a homogenous population does (as observed by the fact that Sweden indeed does have a large amount of immigrants, yet less crime than most nations, the comparison to the US in the previous paragraph being extremely relevant to this point when comparing crime levels as well).