The British press has recently re-started blaming economic migrants for a variety of ills, such as raising unemployment, parasitising on benefits, crime, etc. The Greek press are even worse, with every social wrong being lumped on recent migrants, typically the Albanians. The main characteristic of these views is not that they are racist, but that they are hypocritical. The newspaper editors actually want the immigrants to keep coming in large numbers, but not to acquire legal rights.
Migration of poor people to richer Western societies is neither unwanted nor burdensome to those societies. The immigrants provide a large fraction of the economic surplus that make these societies affluent, as well as the intangible value that makes our societies desirable to live in. In the case of Britain, and even more acutely of Greece, what is today a booming economy would have been moribund without them. In Britain they provide cheap catering, retail, cleaning, and other services, while adding back vibrancy to a society robbed of it by the Victorian regime during the industrial era. In Greece they literally build the country, while restoring a sense of social living, using the health services, public transport, etc, in a country dangerously close to private healthcare, exclusive community and SUV dystopia. The upper and middle classes of Western societies are the main beneficiaries of the immigrants' presence and are in fact delighted that they are here. All this is as it has been with generations of previous immigrants, for at least a century.
The purpose of anti-immigration legislation, and the press campaign required to support it, is not to prevent the influx of immigrants (which must be preserved for the sake of the economy). Immigration could in fact be reduced by a variety of policies different to the actual ones, such as reduced interference in the economies of the source countries, a tighter social network in Western countries (which would resist marginal existence), stricter adherence to labour standards and less appetite for low-wage jobs on both sides, and measures to reduce the exploitable aspect of exporting jobs to poor countries (whose economic effect is the same as for a very marginalised form of migration, so much so that people opt for actual migration to improve their prospects).
Rather, the purpose of anti-immigration legislation is to ensure that immigrants continue to arrive but stay as marginalized as possible. This is not due to any racism or fear of different values, but to ensure that the immigrants will continue to be exploited, and thus produce the goods and services that we want without eventually claiming their share of this surplus. Specifically, we want immigrants to work and preferably pay taxes, but not to claim public services, not to gain political representation, and most of all we do not want them to acquire property here. Property (in land or in business, including semi-tangible business relationships) is what really affords us our superior status as citizens. Immigration law is there to ensure that the immigrants remain labourers, and are are prevented from becoming owners. The Nigerian who staffs the espresso bar next to your city-centre flat late at night may be adding £1000 to its value in the housing market. We want to pocket the £1000, and complain that the espresso should be cheaper and available round the clock.
From a moral point of view, the distinction between "asylum seekers" and "economic migrants" is bizarre. In one case we feel we should not deport someone to where they may be killed or tortured by a regime, which we may or may not have had anything to do with bringing about. In the other case we feel it is OK to deport someone to where they may be killed or injured by economic hardship, malnutrition, or disease, which we may have had a lot to do with bringing about. There's no logic in this other than to ensure that those who come because they are poor are classified as poor and stay that way. There's also no excuse for the practice of allowing skilled professionals to immigrate in preference, for example under specialist worker visas. It's hard to imagine a practice more injurious to the source countries, save perhaps from burning their universities or killing their skilled professionals.
I do not know what would make a comprehensive, rational, migration policy within the current framework of vastly unbalanced and differently regulated First and Third World economies. Unrestricted migration by itself own would create serious problems for both sides, probably more severe for the Third World. I would point at the European Union for an example of a successfully managed liberal migration policy. Excessive or dislocating migration is not an issue in the EU because of the policy of granting (almost) full mutual citizenship rights, as well as an active policy for convergence of the member economies. When these measures were first contemplated, the economic and democratic mismatch between north and south were comparable to the difference today between the West and some common sources of migrants. These lessons should probably be considered when looking for a global migration policy, if equality and global welfare is a goal.