we’d give up on cars? Electricity? Beef? Because having those things, as I like to say, your “hot showers and cold ice cream” is what is destroying this world’s habitability. It’s not just the billionaires but our demand for the shit they sell us, regardless of the economic paradigm that delivers it.

Probably not, but we could get that stuff sustainably. I get what you're saying, and until a couple decades ago this would've been 100% true, but clean energy—the thing we need for our hot showers and cold ice cream—is essentially a solved problem, and it's being solved better and better every day as more advancements are made. Beef and other environmentally destructive consumer products are harder to fix, but it's at least in theory possible to make them more efficiently, eliminate them or replace them with cleaner alternatives. There's a certain amount of destruction that's hard or impossible to eliminate, but multiple times that happens because someone somewhere doesn't want to spend money doing things sustainably (and, more broadly, because the system selects for people who don't do things sustainably). It's less about everyone having a sustainable amount of wealth and more about the people most invested in the status quo (rich stakeholders) being removed from power; imagine the progress that could've been made towards net zero if not for pro-oil lobbying and misinformation for example.

s the world wants more beef, the rainforest gets the axe so ranchers can graze their cattle on its ashes.

Alternatively, the world can only ask for more beef because there's rainforest to cut down. If an external force prevents that from happening, the people who want more beef (and the people who already get a lot of beef) will adapt. Yes, that will make beef less available and therefore more expensive, but then it can be replaced with more sustainable alternatives. First world eating habits don't necessarily need to be kept around in this hypothetical, but that doesn't mean it's impossible to provide everyone with decent quality food; that food will just need to include more vegetables and legumes and less meat.

Let’s say the first world standard of living downgraded just a bit, and the third world standard of living was elevated to first world standards overnight, do you think our demands of the planets resources would diminish?

If this elevation took place under current economic, absolutely not. If, say, concurrently every vehicle and factory was replaced with an alternative based on clean energy, then with small modifications (say, more vegan food and less meat) it's not impossible; even poor countries consume a lot of energy in 2025, and because they don't have the resources to buy, say, solar panels most of it comes from oil instead. It's inefficiencies like these that could and should be reallocated to sustaining the 10 billion people the world population is projected to peak at, but under capitalism it's not profitable for that to happen so it doesn't.

Should have read more of the thread I spawned before responding to your other comments.

So to me, it seems like the real solution is to begin interplanetary colonization.

That doesn't fix the problems on Earth, and I don't want to pretend it does. I also want to be clear that the way that Musk and Bezos seem to envision interplanetary expansion is.....not desirable.

But to me, beginning the Terraforming of Mars is a crucial step in human progress. There's no ecology or biosphere for humans to ruin, but if we can establish a foothold for humans to live there, it let's off the steam valve of humanity on Earth's biosphere and let's us begin the real work of fixing our biosphere without resorting to mass human death.

That probably sounds like a tech-bro pipe dream, and maybe it is, but it also feels like the kind of thing humans will eventually need to do if we want to survive as a species (my main drive for it is so humans can survive the next asteroid, which is a whole issue unto itself).