I think we should donate billions of free clothing articles to the Mexicans...infested with smallpox.
And then after the smell goes away we can open the borders.
Despicable.
Yes, but consider this: the Dutch thought using smallpox as a weapon was despicable, but the Spanish and the Portuguese did not. Not as many people speak Dutch in the Western Hemisphere nowadays, and not as many would be speaking English either if the English-speaking colonists didn't have the stomach for genocide. The reason we shouldn't conquer Latin America isn't because it's "despicable", which it is of course, but because cheap labor is more productive and much more beneficial to the economy when they think they are free. That's what left-wing politics has always been about.
... "the anti-immigrant crowd" ...
I'm very much pro-immigrant, as a matter a fact, but I'm not pro "open borders", at least not when there are other nations that still act within their national self-interest. The only parts of the world that historically have had open borders with complete disregard for national interest have quickly been conquered. (Please don't confuse allowing large-scale immigration, which is what the United States found to be in its interest throughout most of its history, with "open borders" - controls were put in place pretty darn quick once the population density increased.) As a matter a fact, I'd like to see the population of the United States inch toward a billion during the 21st century, so our economy as a whole could stay above that of India, China, the expanded EU, and the Arab League, but this should be done through a merit-based immigration system.
Not if they have no incentive to come here seeking welfare. Then only the responsible and productive people will have any reason to arrive.
There's more to this than just "Welfare" as we know it today, there are the underlying reasons why Welfare was created in the first place, and it cannot be taken away at a stroke of a pen without taking care of those underlying reasons first or the results would be many times more devastating. Many western countries suffered political revolutions mid-way into their entry into the so-called "Industrial Revolution". Those revolutions didn't happen because Karl Marx was such a smartie, they happened because the mob of poor people decided it was easier to loot and pillage than to work their way up through the capitalist system (which admittedly wasn't very fair in those countries and was failing to reform itself, but the revolutions can still happen under the fairest of systems). That's why we have welfare: it costs us less than the damage the mob of angry poor people would cause.
Poor people are dangerous, especially in large quantities, and especially if they are jealous of what you have. True, they have very painful and difficult lives, but everything is relative - compared to our uncivilized ancestors just 5000 years ago their lives are pretty darn good. Gather round, little pro-open-border kiddies, Uncle Alex will tell you a story of how our world might end up in the future:
Imagine a poor person living among other poor people in Indonesia working 60 hours a week attaching zippers to jeans for $3000 a year, which is what the actual value of his labor is on the open market. He is pretty content - he can buy his daily bread, send his children to school, and maybe even buy a used television set. He knows there are rich people somewhere out there, but they are too far away to be angry at, and all of his neighbors live just as well as he does in a poor but happy little community. If they do decide to "beat the rich" and go Communist, so goes Indonesia - the few rich Indonesians flee, and Indonesians find themselves in the middle of a war zone making $500 a year - not that big a loss to the world economy.
Now imagine America has open borders and no socialist government policies. Someone tells this jeans zipper attacher guy that he could make $10,000 a year doing the same work in America, with the increase in salary being due to lower density of cheap labor there (though obviously not as much as before) and also a much larger sales market, which means lower shipping costs for the company. He saves up for a $500 passage for his family on a cargo boat (or buys it on credit), arrives in LA, and indeed does get a job for $10,000 a year. Land costs a lot more, obviously, but his family can rent a cheap room in some cheap housing project too crummy to be allowed to be built back when there was government regulation. He misses his old village and its community, but hey, American dream, right? He works just as hard as he did in Indonesia, makes more money, but for some reason he just isn't happy.
He sees all those rich Americans, most of whom hate him for bring down their own wages. Those people have all the luck - they had free education, tremendous economic protectionism, etc... But now that the playing field is leveled, they're angry at him. He has to join a gang of other Indonesian jeans factory workers for his own protection, and in that gang he hears things: "Americans don't deserve what they have! They still have many economic benefits: savings and land they bought back when they'd be paid $20/hour to do the job we're doing now!" Since America would by then have 100+ million people, mostly recent immigrants, who're making less than $15K/year, this sentiment would be very popular. "The rich people owe us", they would say. Why should some childless American couple have this big house all to themselves, when we, five families with a total of 30 kids, have less living space than they do!" Etc, etc, etc.
The riots won't begin all at once, but once they do they'll accelerate, and, since guns are legal, will become ever more deadly. Factory owners will have to hire security to protect both their factories from sabotage and their workers from the angry mobs of the unemployed. The more violence increases, the worse the economy becomes; and the worse the economy becomes, the more violence increases - the textbook collapse of any country that finds itself having a lot of angry poor people.
America falls further and further behind other nations as various Communist (the "Reds") and anti-Communist (the "Whites") fractions gain local power and fight each-other for broader control. After several years of mass chaos and civil war, the rich will come to see that continuing to fund the Whites is a lost cause, and will instead pay an arm and a leg to immigrate their families to Japan, which kept its immigration merit-based and built zipper-attaching robots a long time ago - and in fact are making their zippers from an alloy mined in the asteroid belt and smelted by throwing it in close orbit of the sun. Japan's scientific innovations in the field of SDI prove especially useful as newly Communist America tries to use its nukes as leverage in negotiating the price on imports of Venus-grown rice to feed its starving masses. In the end, the leaders of America, and all other poor countries in the world, are forced to resort to drastic measures to maintain their hold on power, which some going as far as instituting zero-child policies and evacuating whole parts of their country to sell to the Japanese.
Open borders and free flow of people are good values to have, and in many cases they have utilitarian benefits, but not when taken to extreme. In a contest between blind idealism and pragmatism, in this fairytale symbolized by Japan, pragmatism will win out in the long run.