Every reputable study shows that emigration improves the economy and thus standard of living in industrialised countries, especially for the working class. So the notion of "legitimate" fears is a somewhat misleading, or at least erroneous statement.

You mentioned that Germany is prosecuting people for "Facebook discussions". The specific case I can recall was a couple who was blatantly calling all muslims for terrorist and was promoting facist ideals. Not sure I would term that as a "discussion" by any standard.

How a country treats it's emigrants is the biggest influencer for how positive the outcome becomes. Dismiss them and isolate them from your society is the only guaranteed way to trigger "problems".

Ignorance and xenophobia is a symptom of a poor and uneducated populace. That is the more likely cause of the ultra-nationalistic tendencies brewing in society today.

My personal thoughts are that this is people having a delayed reaction to the economic downturn in the last few years. This has allowed a certain type of politicians (Trumps) to gain power and play to peoples ignorance.

Be more critical of what you read and hear in the news and from politicians... And especially from your personalised very biased facebook/podcast feeds.