With these references the authors betray an inability to face up to the realities of the pressures of burgeoning population on a diminishing resource base. They also fail to address legitimate concerns about the impact of relatively large numbers of immigrants on the most economically vulnerable sectors of our society.
The "brutal truth" (as Sandy Irvine puts it: see his important "The Cornucopia Scam: Contradictions of Sustainable Development" in the latest issue of Wild Earth) that the left is slow to face is that in an age of scarcity, there is no sustainable way to adequately feed, clothe and house all 5.6 billion of us (and growing at about 90 million more per year). Even if by some magic we could instantly put an end to oppression and somehow keep our population from growing appreciably, we would still be using resources at a rate far faster than they can be replenished. There are simply too many of us.
Similarly, instead of excoriating the messenger and burying its head in the sand, the left should proactively seek positive and more humane solutions to the immigration problem. The effect of denial is to leave the field empty to the most xenophobic and racist elements.