Immigration is not the driving factor behind economic instability, although it can add onto it if the conditions aren't right. For instance, allowing uncontrolled waves of migrants from incompatible cultures is a particularly bad idea, because it prevents migrants from settling to the new culture, and puts strain on the economy. Whereas controlled migration can greatly benefit a culture. Some have objected to controlled migration on the basis of libertarian philosophy, however, this is misguided.
“In a libertarian society, there is no commons or public space. There are property lines, not borders. When it comes to real property and physical movement across such real property, there are owners, guests, licensees, business invitees, and trespassers – not legal and illegal immigrants.” – Jeff Deist
Of course, some insist that the free movement of peoples is a good thing, however, uncontrolled migration is a provably disaster. Of course, one charge made against opponents of uncontrolled migration is that they are racists and xenophobes. Whilst some opponents of migration might oppose all forms of immigration, and might genuinely be racist and or xenophobic, this does nothing to undermine the case for controlled migration. Uncontrolled migration is a palpable disaster, and this is very easy to show.
Now, whilst racists and xenophobes have seized on this to push for their agenda, it does not undermine the case for controlled migration. To argue otherwise would to be to commit a guilt by association fallacy. Moreover, trying to silence people and labelling everybody who disagrees with you as racists does nothing to combat the views of actual racists, et al. It just breeds resentment and allows extremist views to take further hold amongst those who otherwise might not have considered such views. The reason Donald Trump is so popular is because of the sheer devastation the political elites have wrought and the sheer contempt they have for poor and working class people. People are pissed off about being spat on and treated with contempt. Political correctness, etc. made Donald Trump possible.
Free trade is also a bedrock of economic prosperity. Voluntary and exchange and interaction is simply what trade is. Whenever the government gets in the way, certain interactions are prohibited, others are forced, and money is lost on bureaucracy and waste. And since the government is inherently corrupt to its very core and only interested in maintaining power, it bends to the will of those who back them financially, and end up passing legislation favourable to said parties. This results in artificial monopolies, and mega-corporations who no longer to have to compete fairly. Prices go up, and smaller businesses have to close. Jobs are lost as a result.
Now, what arguments are there against these positions? The most popular anti-immigration argument is that immigrants 'steal jobs.' This is, of course, false. Unless you have been fired and had your job replaced by an immigrant, then, no, nobody is 'stealing' your jobs. Immigrants come to a country and get hired. This is somehow considered problematic. Of course, unemployment is rising, and there aren't enough jobs to go around. Except the reason for low jobs and high unemployment is because of government intervention, not immigration.
The obvious solution is to end the economically suicidal policies that lead to high unemployment, etc. and you don't fix the economy by "creating" jobs, you create jobs by fixing the economy. It really is that simple. Moreover, if there are no jobs, then there are no jobs for immigrants to steal. As a side note, some of the staunchest anti-immigration pundits in the US are sons of immigrants, some of whom entered the US in a not entirely legal way. It also worth noting that the biggest anti-immigration voices have never worked the kind of jobs that immigrants typically work.
Opening the borders and doing away with all regulations immediately without making any changes to the disastrous and economically suicidal policies currently being employed might be irresponsible. Refusing to change those disastrous and economically suicidal policies and maintaining closed/regulated borders is far worse, however. Now, the correct approach to 'fixing the problems' is not clear, since it depends on how one views things. Either, we do away with everything in well fell swoop, which would cause a massive restructuring of society, or we implement fixes incrementally, to reduce the upheaval caused by fixing the hideously broken system we have. In other words, the difference between ripping off a plaster, or peeling it off slowly. Yet, it is certain, clear, and obvious what the correct stances and policies should be.
Essentially, focusing on immigration is a red herring, since the cause of economic stagnation has nothing to do with immigrants. Opposing free trade, on the other hand, is to oppose economic stability, recovery, and growth. It is no coincidence that some of the biggest anti-immigration voices are staunchly opposed to free trade, and support higher taxes. This is simply backwards thinking that will make our economic woes worse. For more, see: http://reason.com/archives/2015/08/24/the-trump-recession