Dutch academics have researched the economic effects of immigration.
Report: http://www.demo-demo.nl/files/Grenze...gingsstaat.pdf
(you can download and translate it here: https://translate.google.com/?sl=auto&tl=en&op=docs)
Long story short:
They conclude the net costs have been over 400 billion in the past 25 years. The upcoming years this will increase to 600 billion. Which is huge for a country as small as holland (The current dutch national BNP is 900 billion). And do note; this is net cost, AFTER the benefits of immigration.
Is this to continue, the dutch wellfare state (social securities, cheap healthcare) will come under serious pressure. Which leads us to the following discussion:
At which point should a country say: "Ok, halt the immigration, otherwise we cant maintain the current social systems in place and the whole country will suffer the consequences?". Or in other words; should a country give up its wealth and social securities in order to facilitate (economic) immigration?