We found out today, when Bernie Sanders dismissed the idea of open borders as "a Koch brothers proposal." The responses were telling:
It's not at all surprising that liberals would respond to Sanders critically: liberal border policy is, after all, the orthodox liberal position. But what's extremely telling here is that the overwhelming majority of liberal critics aren't actually invoking the liberal critique of borders; instead, they're invoking the decidedly right-wing case for global capitalism.
ICYMI: Historically, the liberal critique of borders didn't turn on economic arguments. It was ordinarily advanced as a human rights critique, one which relies on a "freedom of movement" that states have no right to restrict. This right has never been a particularly visible stake in American political discourse, except perhaps among the radical left -- but it's a live and contentious issue in most of the rest of the world, where national borders and border issues are far more prevalent. And its argument is woven all throughout the fabric of liberal thought; it's closely related to popular civil rights arguments against unlawful detention, and appeals intuitively to all kinds of liberal notions about liberty and human rights. It's the basis of all kinds of liberal causes, though their partisans may not recognize this; it's why liberals have opposed the Berlin Wall, the West Bank barrier, and so on.
The implications for the debate over the US's border [read: with Mexico] are obvious. However convenient or advantageous a closed border might be, the US government simply has no right to enforce it. People have every right to travel to the US for any reason they like; the idea of armed government agents preventing poor migrant workers from simply stepping across a line is monstrous and completely antithetical to basic US ideals.
This (or something like it) is roughly the objection to Sanders' comments being voiced by the US left, and one would expect liberals to enthusiastically join them.
But instead, as noted above, the overwhelming majority of liberals have rallied around a different attack. Their argument is not that immigrants have a right to cross over into the US, but that allowing them to do so would be economically beneficial. This, of course, is the argument of global capitalism: the best way to redistribute wealth internationally is to rely on markets. That way, it will inevitably trickle down from the rich to the poor. Expanding the labor pool may give employers leverage to drive down wages and erode workplace protections, but surely that trend will be negated by all of the shared prosperity, since the market guarantees optimal outcomes for workers and employers alike.
Suffice to say that the left has never been particularly sympathetic to this argument. Even those who favor the abolition of borders on human rights grounds are under no illusions about how global capitalism exploits labor migration to improve its bargaining position, evade democratic governance and consolidate the power of the rich. This has been a central critique of modern leftism for decades, inspiring writers from Chomsky to Klein and animating movements from the NATO protests to the World Social Forum counter-protests.
More importantly, the left has always understood global capitalism as one of the primary drivers of global racism, serving as a mechanism to assert white supremacy over the mostly nonwhite global poor. After all, America's wealth was in part built on the backs of Mexican slaves; to leverage their poverty as an opportunity for cheap labor and pretend that they're better off under the exploitation of rich white men than they would be if we just paid them what we owe them is a direct and transparent extension of our country's continuing legacy of racism. This dynamic is present wherever the engines of international capitalism have funneled the profits of cheap labor into the pockets of the rich.
This, if anything, is what the left means when it talks about the role that economics plays in racism. It is a role intrinsic to the logic and agenda of capitalism itself.
So what, then do, liberals mean? They have made a play for the center-left by soberly agreeing that yes, race does have an economic dimension -- but at the same time, the people who concede this are precisely the people who think that immigrants would be better off if we let the Kochs exploit them. So if capitalism isn't the problem, what is? Perhaps opposition to capitalism?