"Indians qua Indians" apparently fell under the "math is hard!" category of "this is fantasy; I'm certainly not going to do research for it!"

The problem isn't exactly with "eliminating the Indians." It's with eliminating the Indians... and claiming that the US would've developed the same anyway, except for the place names and they'd use wheat instead of corn.

xiphias is collecting speculation on how things would be different, with the main point being: No Native Americans = no "American frontier" a la Little House on the Prarie.