I reject Malthus' picture of pre-Columbian America for the same reason I reject Lysenko's account of evolution.

Lysenko was motivated by politics. Baez was motivated by politics.

Physics improves, but history deteriorates. Those writers closest to events give us the most accurate picture, while later writers merely add political spin. Since 1830, history has suffered increasingly drastic, frequent, and outrageous politically motivated rewrites, has become more and more subject to a single monolithic political view, uniformly applied to all history books written in a particular period.

If you read old histories, they explain that they know such and such, because of such and such. If you read later histories, then when they disagree with older histories, check the evidence cited by older histories, you usually find that the newer histories are making stuff up. The older history says X said Y, and quotes him. The newer history say that X said B, and fails to quote him, or fails to quote him in context, or just simply asserts B, without any explanation as to how they can possibly know B.

And because it's generally acknowledged within anthropological, archaeological and historical fields now that modern research bears out a picture of generally healthy, sustainable populations for most of the foragers of the Americas?

How exactly does this modern research reconstruct the life of American foragers centuries ago, and based on what evidence? Could you cite some of this work? (I'd like to see the original work that presumably explains its methodology rigorously, not popular summaries.)

I also note that you haven't answered Wei Dai's question.

Regarding Malthus and de Vaca, you say:

Malthus *seriously misrepresents Cabeza de Vaca's case -- the Floridians were in a bad way, but they were also right next door to Spanish early conquest -- his accounts of the Coahuiltecs of coastal and inland Texas describe them as a healthy and prosperous people...

Here is a translation of de Vaca's original account:
http://www.pbs.org/weta/thewest/resources/archives/one/cabeza.htm

On closer look, it turns out that de Vaca's description cited by Malthus actually refers to a people from southeastern Texas, not Florida. So while Malthus apparently mixed up the location by accident, his summary is otherwise accurate. Your above claims are therefore completely incorrect -- the description is in fact of a people from Texas, living very far from the boundary of Spanish conquest at the time.

For reference, I quote de Vaca's account at length (all emphasis mine):

• Castillo and Estevanico went inland to the Iguaces. [...] Their principal food are two or three kinds of roots, which they hunt for all over the land; they are very unhealthy, inflating, and it takes two days to roast them. Many are very bitter, and with all that they are gathered with difficulty. But those people are so much exposed to starvation that these roots are to them indispensable and they walk two and three leagues to obtain them. Now and then they kill deer and at times get a fish, but this is so little and their hunger so great that they eat spiders and ant eggs, worms, lizards and salamanders and serpents, also vipers the bite of which is deadly. They swallow earth and wood, and all they can get, the dung of deer and more things I do not mention; and I verily believe, from what I saw, that if there were any stones in the country they would eat them also. They preserve the bones of the fish they eat, of snakes and other animals, to pulverize them and eat the powder. [...] Their best times are when "tunas" (prickly pears) are ripe, because then they have plenty to eat and spend the time in dancing and eating day and night. [...] While with them it happened many times that we were three or four days without food. Then, in order to cheer us, they would tell us not to despair, since we would have tunas very soon and eat much and drink their juice and get big stomachs and be merry, contented and without hunger. But from the day they said it to the season of the tunas there would still elapse five or six months, and we had to wait that long.

Also, regarding this:

Boas actually travelled to the civilizations he wrote about, lived among them, recorded their oral traditions and analyzed their languages, investigated their history and their environmental circumstances. For many people, especially in the Northwest, far North and other relatively late-contacted areas, these events occured within the living memory of their elders.

Earlier you claimed that the native population of the entire American continent was devastated by epidemics immediately after the first European contacts in the late 15th/early 16th century, so that even the accounts of very early European explorers who traveled deep into the continent ahead of European colonization do not present an accurate picture of the native foragers' good life they had lived before that. But now you claim that in the late 19th century, this good life was still within living memory for some of them.

It seems like you're accepting or discounting evidence selectively. I can't believe that all those accounts cited by Malthus refer to societies devastated by epidemics ahead of European contact, but on the other hand, the pre-epidemic good times were still within living memory for the people studied by Boaz centuries later.

Most of your resource base collapses because one person is going to have to work MUCH harder to provide enough food for themselves -- fields go unplanted, vegetables don't get tended, wild game is much more dangerous to hunt by oneself, and one cannot expect any assistance with gathering. Even a small number of people used to an agriculture-enriched lifestyle are going to be hit much harder.

Both Clark and Tainter (Collapse of Complex Civilizations) disagree with this claim as stated. A massive reduction in the population means that the survivors get increased per-capitas because the survivors move way back along the diminishing marginal returns curve and now have more low-hanging fruit (sometimes literally). In fact, Tainter argues that complexity often collapses because the collapse is the only way to increase per-capita wealth. Hunter-gatherers spend much less time per calorie than do advanced agriculturalists eg.

The surprise here is that while there is wild variation across forager and shifting cultivation societies, many of them had food production systems which yielded much larger numbers of calories per hour of labor than English agriculture in 1800, at a time when labor productivity in English agriculture was probably the highest in Europe. In 1800 the total value of output per man-hour in English agriculture was 6.6 pence, which would buy 3,600 kilocalories of flour but only 1,800 kilocalories of fats and 1,300 kilocalories of meat. Assuming English farm output was then half grains, onequarter fats, and one-quarter meat, this implies an output of 2,600 calories per worker-hour on average.32 Since the average person ate 2,300 kilocalories per day (table 3.6), each farm worker fed eleven people, so labor productivity was very high in England. Table 3.13 shows in comparison the energy yields of foraging and shifting cultivation societies per worker-hour. The range in labor productivities is huge, but the minimum average labor productivity, that for the Ache in Paraguay, is 1,985 kilocalories per hour, not much below England in 1800. The median yield per labor hour, 6,042 kilocalories, is more than double English labor productivity.

Or

...ranging from a modest 1,452 kilocalories per person per day for the Yanomamo of Brazil to a kingly 3,827 kilocalories per person per day for the Ache of Paraguay. Some of this is undoubtedly the result of errors in measuring food consumption. But the median is 2,340, implying that hunter-gatherers and subsistence agriculturalists ate as many calories as the median person in England or Belgium circa 1800. Primitive man ate well compared with one of the richest societies in the world in 1800. Indeed British farm laborers by 1863 had just reached the median consumption of these forager and subsistence societies.

(Quotes brought to you by my Evernote; it's a pain in the ass to excerpt all the important bits from a book, but it certainly pays off later if you want to cite it for various assertions.)