Mainstream environmental organizations like Friends of the Earth are signatories to that demand: https://www.peoplesdemands.org. So is Rashida Tlaib's office. A group with a similar platform counts the Sierra Club as among the leadership: https://peoplesclimate.org/platform.

Of course nobody speaks for the "climate justice movement" categorically, in the same way as nobody speaks for "conservatism" or "progressiveism" as a movement. But if someone had said in 2008 that ACA was a stepping stone to Medicare for All, would that have been inaccurate?

Putting it another way: I don't think market-oriented environmentalists--for whom averting climate change is a matter of appropriately pricing carbon externalities--are driving the bus of that movement anymore.

Friends of the Earth appears to be an organization that split from the Sierra Club because it wasn't environmentally radical enough. I care about the environment and about social justice. Why would you think "The People's Demands" speaks for me?

Rashida Tlaib supports Scandinavian social democratic policies, and supports this website. But she'd support the social democratic policies either way. I agree with you and not with her (on Scandinavian social policies applied to the US), but her support for this website is not really evidence for it being representative of the mainstream; Tlaib is herself not even representative of the mainstream of her own party. That's why they call her, Omar, and AOC "the Squad".

So to rephrase my question: do you really believe the majority of people who believe we should make tradeoffs in our economy to favor combating climate change also believe in the nonsense in this People's Demands site? Because that's what you sort of directly implied.

I don’t think that’s an implication of what I wrote. The majority may not buy into all the ideas of climate justice, but you can’t tell how coalitions will shake out, or what compromises the majority will be willing to make to protect its coalition. And you don’t know what the next battlefield will be. The question isn’t do you think the majority believes in that stuff, it’s whether you trust the majority to protect free markets at the cost of its coalition, or to stop once necessary changes have been achieved.