To have that position you basically need to reconcile two positions that to me aren't really compatible, unless someone explains it to me.
Either it's fine for Earth to not have humans and just exist peacefully with the rest of the ecosystem until another lifeform takes over.
Or it's not fine for the Earth to have no more humans and so we need to stop climate change from making the Earth uninhabitable for us, but if to do that we want to reduce the humans, I don't get it.
To "kill" humans to save humans seems weird. I guess you can slide on the scale of "more people living worse", or "less people living better", but to choose who is not possible in my opinion, so this is not implementable.
Because if you care about the Earth primarily, then warming or not doesn't really matter, it's just a geological event like many more gnarly ones over the history of meteorite impacts and so on.
But if you care primarily about the humans, then how can the answer be to have less of them? And pick and choose who gets to reproduce?
Population is already naturally decreasing in a fair number of countries. Let's embrace this instead of panicking and trying to reverse the trend.
The bulk of what I value about the future of humanity is our continued existence and collective ability to do beautiful and impressive things together, not the individual existence of some as-yet-unborn hypothetical humans in that future. I don't think humanity's output scales linearly with population and I don't think there's much moral worth to future individuals outside their general contribution to wider human civilisation.
There is no consistent way environmentalists can argue their way out of this particular point you made:
> But if you care primarily about the humans, then how can the answer be to have less of them? And pick and choose who gets to reproduce?
To somebody else it means just living life.
There is no way to objectively argue superiority of one over the other except from a religious worldview.
If you care about the well being of dogs, how can the answer be to have less of them crammed in your tiny apartment?
It’s about balance. It is not true that more of something is unambiguously good, for itself or the system as a whole.
You should read about how reintroducing wolves, a carnivore that kills other animals, made the Yellowstone ecosystem flourish.
https://www.yellowstonepark.com/things-to-do/wildlife/wolf-r...
Or the case of Macquarie Island.
https://archive.is/2020.10.21-044800/https://www.nytimes.com...
Or the deer of Manitou Island.
https://www.interlochenpublicradio.org/2022-03-04/unnatural-...
Or, or, or. We have tons of examples.
Regarding the superiority of worldviews, sure, subjectivity applies and we could go down the rabbit hole of discussing that - but the comment I was replying to was not about which worldview was better! Vasco said that "Either it's fine for Earth to not have humans ... Or it's not fine ... but if to do that we want to reduce the humans, I don't get it." I'm not going to argue that my values are the best because it's already self-evident to me and I doubt I can improve on the existing work[0], but I am very willing to explain how they're logically consistent.
[0] Via utilitarianism and the repugnant conclusion and onward. I don't think I can do any better than all the philosophers who've debated this.
I mean, you might as well quote me a list of your very personal niche hobbies and the importance of keeping them up as some kind of tradition humanity needs to uphold.
I don't think such a line of argument holds very tight in the grand scheme of things.
To others, enjoying the company of their own children and grandchildren (some of the most commonly shared joys across people, in contrast to niche interests) are far higher up there on their list of priorities of things that make our existence worthwile.
Likewise, utilitarianism won't get you far since the other person must first subscribe to it as a good idea. I don't care about "the greatest good for the majority" in some kind of vague sense whatever it means, if subjectively it means no good to me.