Arguably, it is the young people in a society who are most concerned with these long-run environmental impacts. If there's going to be a political (and scientific and technological) mobilization to address them, it's going to require young people.
EDIT:
And we can't get too far down this road before asking the question: Are humans fundamentally a bad thing or a good thing?
This is obviously subjective. But if we say some things have intrinsic value, such as the quantity and diversity of life, then we can make some progress:
From Gaia's perspective, if humans evolved, wiped out a bunch of species, then disappeared, then humans are like an asteroid. Bad at first, but ultimately just changed the direction of evolution, not the actual presence or absence of life.
BUT, if humans are able to go beyond the Earth and establish niches for life beyond Earth, then from Gaia's perspective, humans are a net-good. Sure, there's a lot of terrible habitat destruction as humans become a technological species capable of interplanetary travel, but now humans are capable of seeding life far beyond what other species have been capable of. Humans could create diverse, rich niches for life on other planets and moons that otherwise would never experience life. Humans would then be a net-good.
That becomes impossible if we just view humanity's impact in a zero- or negative-sum way. The more humans, the worse it is for life. BUT 10 billion may be just about the minimum needed to support a large-scale interplanetary capability that's able to establish a foothold for life to flourish across the solar system and eventually the galaxy. Therefore: have children! And reduce your impact on the Earth by eating smart and using efficient energy and transportation options.