Liberals and progressives applauding today's immigration announcement by the Obama administration would do well to read this classic 2004 essay by David Goodhart, the founder and for years editor of the left-leaning British magazine, Prospect.
The diversity, individualism and mobility that characterise developed economies - especially in the era of globalisation - mean that more of our lives is spent among strangers. Ever since the invention of agriculture 10,000 years ago, humans have been used to dealing with people from beyond their own extended kin groups. The difference now in a developed country such as Britain is that we not only live among stranger citizens but we must share with them. We share public services and parts of our income in the welfare state, we share public spaces in towns and cities where we are squashed together on buses, trains and tubes, and we share in a democratic conversation - filtered by the media - about the collective choices we wish to make. All such acts of sharing are more smoothly and generously negotiated if we can take for granted a limited set of common values and assumptions. But as Britain becomes more diverse that common culture is being eroded.
And therein lies one of the central dilemmas of political life in developed societies: sharing and solidarity can conflict with diversity. This is an especially acute dilemma for progressives who want plenty of both solidarity (high social cohesion and generous welfare paid out of a progressive tax system) and diversity (equal respect for a wide range of peoples, values and ways of life). The tension between the two values is a reminder that serious politics is about trade-offs. It also suggests that the left's recent love affair with diversity may come at the expense of the values and even the people that it once championed.