Economists aren't known for their coherency as a profession, but on immigration, they tend to agree. As far as the economic case is concerned, migration is a winner for all countries involved, at least in the medium to long-term. One paper in the Journal of Economic Perspectives concludes that removing all barriers to labour mobility would increase global output by 67 to 147 per cent.
So when US mega think tank Heritage released a report attacking the benefits of immigration, it's not surprising to see the findings set upon by all sides. One of the most amusing fiskings of Heritage's work places their 2013 paper against work published by Heritage in 2006. The comparison is stark, and thrashes the claims of this new research. The author of the 2006 report has slammed the study's findings:
Unless they expect readers to believe all this household income (a) generates no productive work (e.g., makes product, mows lawns, nurses the sick, and starts businesses that hire other Americans) and (b) is 100% remitted abroad, consuming nothing in the U.S. macro economy, then the report is misleading.
Turn to the UK, and sadly many will make similar claims in denying the economic benefits of immigration. But data from the new Business for New Europe group suggests that migrants are an economic boon:
Between 2004 and 2009, migrants from the new EU member states added £5bn to the UK economy, the group says, noting that incomers are net contributors to the state.
It's not surprising that migrants would be net contributors. The widely stated but less often backed up assertion that people move to the UK for the cushy benefits does not seem to hold up under scrutiny. Indeed, the vast majority of asylum seekers don't seem to know a welfare state exists (so it's unlikely that they intend to exploit it):
The vast majority of research participants were working in their country of origin and most expected that they would be able to work in order to support themselves and their families when they came to the UK. Very few were aware that they would not be allowed to work when they came to the UK. They only became aware that this was the situation after they arrived.
The majority of respondents (around three quarters) had no knowledge of welfare benefits and support before coming to the UK. Most came from countries lacking well-developed welfare systems and had no expectation that they would be supported. Some were disapproving of the welfare system. There is no evidence that respondents consider the UK welfare system to be more generous than that of other countries.
Migration is also a powerful tool to propel the development of less developed nations. One study of New Zealand's Recognized Seasonal Employer program saw communities in Tonga and Vanuatu benefit, as those who emigrated sent back large amounts in remittances:
So what have immigrants done for us? If you care about growth, quite a lot, and there's potential for even greater gains by freeing up movement further.