I'm probably not going to debunk it either, not by any real standards. But...
It seems to me that our level of technology has increased, partly through new discoveries, partly through new ways of applying those discoveries, but also at least partly through increased specialization. You've got a farmer growing huge amounts of food. But that's because there's a tractor factory, and the tractors are smart because of the chips in them, and the chips connect to the GPS satellites in orbit. To make that work, you need more than the farmer. You need the workers in the tractor factory, but also the workers in the chip plant in Taiwan, and the chip factory needs the equipment manufacturer in the Netherlands. And you need the rocket manufacturers so you can put GPS satellites in orbit. And the rocket fuel manufacturers. And so on. It basically has taken a globally integrated material culture to achieve that level of productivity on the part of the individual farmer. Which we can do, because the farmers are so productive that we don't have to spend very many people on farming.
A fair chunk of the progress of the last 200 years has been made possible by increasing scales of integration. But I worry, because we're running out of globe to integrate. (Africa, maybe?)
So, back to Mars. Yeah, none of this proves that 1000 people couldn't be self-sustaining. But for them to do that, they'd need a fair amount of tools. And that means that they'd need someone who knows how to repair and/or replace every one of those tools (and any tools they use in the process). And there's a hard cutoff below which they cannot fall, due to the need for oxygen. They can't just fall back to being hunter-gatherers.
So, yeah, I didn't debunk it. But, seriously, what's the maximum number of sophisticated kinds of machines that 1000 people can run and maintain? 100? 500? Can you build a self-sustaining colony on Mars with only 500 kinds of machines?