I think this comes from vastly underestimating the value humans bring to other life. I would argue that without humans there is no life. We are the only species in the planet that has, in the next couple million years, the ability to allow life to expand throughout the universe. We are literally the only species alive that can do this. Without us life is frail and subject to the whims of cosmic events on our planet that could whipe it out. Humans bring a lot of value to the world and I think we play a critical role in the history of life. I find that people who argue against humans using earths resources forget that we have a very important role in the ecosystem. So important in fact, that a the extinction of a couple thousand of species and habitats is probably a small price to pay for us to learn how to use our incredible ability to control the environment.
I think you're overly optimistic. Our technology does and will explore space at large.
Humans in space (beside the few scientific missions and maybe a Mars trip) make about as much sense as motorized fishbowls on highways. Humans won't leave the solar system, and we may destroy the ecosystem that feeds us before we can start a serious space expansion program.
Beside the CO2 problems (warming and ocean acidification), we've also destroyed a third of arable land in the last 40 years. The presence of biodiversity is needed for resilient ecosystems too.
