When it comes to whether and how to regulate the economy, western societies have a history of liberal theory upon which to rely. But when it comes to immigration, there is not much in the liberal tradition to which they can turn. As a result, in both Europe and the United States, much of the debate over immigration is dominated by illiberal voices, the most insistent belonging to politicians who promise to protect the cultural integrity of the homeland against the presumed degeneracy of the alien.

Xenophobia is an illiberal response to immigration from the right, but multiculturalism represents much the same thing from the left. Many multicultural theorists, although committed to openness toward immigrants, are not committed to the openness of immigrants to their new home. For them, newcomers, living in an environment hostile to their way of life, need to preserve the cultural practices they bring with them, even if some of those practices conflict with liberal principles. Group survival counts more than individual rights in the moral accounting of many multiculturalists.

One way to maintain a commitment to openness when addressing the vexing question of national borders is to recognise that cosmopolitanism is a two-way street. From this perspective, it is unfair that someone who happens to be born in the US is likely to live longer and better than someone born in Kenya. This does not mean that the US must open its borders to everyone from Kenya. But it does mean that a New Yorker should recognise that any advantages he may have over a Nairobian are due to an accident of birth rather than merit.

But embracing cosmopolitanism also means that once a society admits new members, those members are obliged to open themselves to their new society. Multiculturalists are reluctant to endorse this part of the cosmopolitan bargain, but liberals must.

One can understand why, living in a foreign country they may perceive as hostile, immigrants opt to close themselves off, and some host countries — France, for example — may be too hasty in demanding that immigrants accept new ways of life. But attempting to live a closed life in an open society is bound to be self-defeating and not something a liberal society should encourage.

An instructive example of the cosmopolitanism bargain came in 2006, when Great Britain’s then foreign minister, Jack Straw, raised concerns about the hijab, the full-head covering worn by some Muslim women.

He was not making a xenophobic argument that Muslims do not belong in Great Britain, or a multiculturalist argument that Muslims should be allowed to wear whatever traditional garb they believe best expresses their cultural and religious sensibilities. Nor was he asking for the full assimilation of immigrants to British customs. He was only illustrating what it means to be open to others while expecting openness in return.

Some argued that, in suggesting to Muslim women what they should wear, Straw was interfering with religious freedom. In fact, liberal values sometimes contradict each other. Islam, for example, has historically permitted certain forms of polygamy, but no liberal society is obliged to extend religious freedom in ways that undermine its commitment to gender equality.

Fortunately, Straw’s example does not pose such a sharp dilemma. As he pointed out, wearing the hijab is not commanded by the Quran and represents a cultural choice, not a religious duty. For liberals, the question is never whether borders should be completely open or closed; a society open to all would have no rights worth protecting, while a society closed to all would have no rights worth emulating.

A liberal society will view the world as teeming with potential that, however threatening to ways of life that are taken for granted, forces people to adapt to new challenges rather than trying to protect themselves against the foreign and unknown.

Finally, a liberal society will not focus on what we can offer immigrants, but on what they can offer us. The goal of openness implied by immigration is worth preserving, especially if both its demands and its promise apply across the board.

Guardian