You raise some interesting points until you got here. Most of the plains and eastern tribes used dogs as beasts of burden (and meals) long before whitey showed up. In the southern end of the continent, the Incas used Llamas and Alpacas. In what is now North Dakota, the Mandan raised chickens.
I always get a kick out of how backward Europeans look at out native peoples. The Aztec and Maya cities are legendary for their work with precious metals, cement and medicine. Both civilizations were rotting from within by the time whitey showed up.
Even in the less civilized tribes of North America, there was a trading culture far more advanced than is realized. Tools and metal artifact of eastern tribal design have been found in central North Dakota burial mounds. The Navajo originally came from Alaska. The Chippewa were originally pushed out of the Finger Lakes region of New York by the Seneca and eventually made it to Wisconsin and Minnesota to push out the Sioux who, in turn, moved to the Dakotas to displace the Mandan and others . . . again long before whitey showed up.
Certainly whitey brought more diseases into the mix, but he also took a few back to Europe with him, as you pointed out. The whole point of Steyn's article (as well as our exchange about the exchange of diseases) is to show that the so-called experts don't know squat.
Years ago, in a past life, I had a job which brought me in contact with a lot of these people. I learned a lot of interesting stuff including this account of Tehcumseh's curse.
Fair enough. I was aware of the llama, alpaca and dogs being present in America. Also I believe the Muscovy duck and turkeys were domesticated in Mesoamerica.
My point stands, however. Most of the major epidemic diseases come from domesticated herd animals such as pigs, sheep, horses and cattle. The Indians had none of these animals and therefore no exposure to the diseases we contracted from being in constant contact with them.
There is also some evidence that pureblood Indians have a narrower range of immune responses, probably due to "genetic bottleneck" created by Indians being descended from a small group.
I suspect you are wrong about the Mandans raising chickens. Possibly when Lewis and Clark arrived, not before Columbus, as I believe chickens are native to SE Asia, not South Dakota.
I don't believe Indians were backward. The more we look, the more complex and varied their societies are found to be.
A single plague, the Black Death, in medieval Europe killed about 1/4 to 1/3 of the population and caused massive social disruption for the next century or so.
Consider the effects of plague after plague with equivalent or greater death rates. Most of the Indians the white man ran into were basically refugees from broken societies.
Chickens are derived from the jungle fowl of another continent... not North America.