The logic of immigration goes something like this. Business needs labor, opening the door to immigration brings in labor which helps meet the needs of business, generates new businesses, and gives everyone a better life.
Businesses decide it's cheaper to do business in the unregulated third world where they'll be able to hire the same exact employees they're getting here for a fraction of the wages and without the taxes or social services they have to provide here. The immigrants however remain behind becoming an even bigger burden to the state, which raises taxes even further and drives more businesses overseas, creating a cycle of job losses and social problems, that can't be broken until immigration, tax or social welfare policies change.
Immigration properly handled can be a boon, however two major factors have turned immigration into a loss. First of all the quality of immigrants has dropped a great deal. Today the same Irish immigrants who built up America have trouble getting in the Golden Door against the press of Third World immigrants. Yet it's clear which group has more to offer and which will take less and give more back.
Secondly the expanding matrix of social services expands costs on local communities and governments, which are then passed along to businesses and working class people. Immigration then serves to precipitate depression.
Since capitalist systems naturally run in boom and bust cycles, but immigration policy does not, the system is set up to insure a surplus of immigrants that will quickly become a crime wave during the bust part of the cycle. The social problems created by this can be seen in virtually every major urban city. The problem is worse in Europe as the recent Paris riots demonstrated.
Immigration only works when there is social and economic mobility. Surplus immigration however creates a permanent underclass with the accompanying rage, violence and cultural assaults of an angry underclass.
The problem is that immigration has stopped being an economic process, and become a political one. Slogans such as "A Nation of Immigrants" only worsen the problem by treating immigration as inevitable, rather than a choice.
When a political process supersedes an economic one, the result is inefficiency and general chaos. That is the status of immigration today. Since the days when Tammany Hall first discovered that immigrants were a fantastic asset for voting in Democratic politicians, immigrants have become a handy tool for liberal politicians looking to maintain a plantation voting base. The logic behind immigration remains that same political logic, "if we let them, they will vote for us". (Not that conservative politicians are immune from this type of thinking either.)
Immigration has become a poorly structured and politicized process, and the result is that the high cost of immigration only continues to grow. Businesses which are given the choice between employing Pedro or Ahmed for 12 dollars an hour in America or 12 cents an hour at home, will make the perfectly logical economic decision to move abroad. And businesses that don't, as well as ordinary Americans will be stuck with the social health and welfare costs for Pedro and Ahmed's extended families.
This situation naturally results in a large demand for undocumented immigrants who can be paid much less. However typically even undocumented immigrants have families who add to the social health and welfare costs, even more so than legal immigrants as they have fewer job options and less likelihood of possessing the skills or literacy to get a better paying job. And of course undocumented immigrants are far more likely to engage in criminal activities.
This kind of self-defeating process can't go on indefinitely, but it can go on long enough to destroy social and business structures, while creating a massive welfare state, extremes of social instability and commonplace crime and violence. The way forward is to reform immigration, to view it as a job interview rather than a sovereign right, and to bring in only what the country can support, not only for today's economic boom, but for tomorrow's economic bust as well.