Philippe Legrain makes a compelling argument for why countries should open their borders and allow immigrants to freely flow between countries. If not open the borders completely, at least allow more free flow of immigrants than what we currently have. He uses examples of how Israel took in a million immigrants in the 1990's and assimilated them into society without much of an issue. He also looks at models of multiculturalism that Canada has in accepting people from all over the world.
Much of what Philippe Legrain argues for has merits based on research and data given by researchers across the world. He has also provided stories and interviews of people who explain from their own personal views of the advantages of opening borders and breaking down the stereotypes and bigotry that is out there in our society. I really like that he tries to look at many different cultures and countries to see how they each handle immigration differently, from North America, Europe, to Australia.
There are good arguments that opening up borders will help the flow of immigration and raise the standard of living for many people around the world, both in rich and poor countries. Obviously, since this book has been written, there is a lot of additional data out there that would help continue the argument that is made in this book.
One of the main issues that Philippe Legrain does not expand on and that he admits himself that he's not an expert in, is the impact of religion clashing within western societies. He tries to do his best in the last couple chapters of the book to explain about Islam and make his case for how religions can co-exist in Western culture. This though, I believe requires a lot of additional research. One can make an argument for opening borders and that religion shouldn't be an issue, but how society reacts and handles these issues is a whole different story. There is still much debate on this topic that needs to be had if borders should be opened up and multiculturalism to succeed.