Your belief seems to be that the value of humanity scales relative to the number of living humans. I disagree - I don't think one billion humans would be 1/10th as valuable as ten billion humans, provided we got to one billion just by deciding to have fewer kids. Killing humans is morally wrong in everything except weird edge cases, but having two children instead of three is not killing anyone.
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.
What you are missing is that to you, "valuable" continued existence means continuing to produce pointless tech gadgets and indefinitely increasing global GDP or something.
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.
I don't care about useless gadgets and GDP. I care about people poking around in the Mariana Trench, surveying carnivorous snails, writing and reading novels, and keeping their societies functioning and happy. Please don't damn me for opinions I don't actually hold.
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.
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.