eugenics is gross

First and foremost, I was never talking about eugenics (a thing that would mean "selective breeding", definitely not the thing I'm defending). It's about other topics seen "as controversial as it" (although even the visible, blatant climate change is still seen as "controversial" by negationists in an anthropocentric world), which I guess will become clearer at the next paragraphs.

you’re wrong that there are too many people for the earth to support

While indeed Earth physically supports way more humans, don't forget that humans were never the center of the biosphere: there are trees, algae, jaguars, owls, spiders, ants, bears, bacteria, protozoa, complex and beautiful sea life, and so on. We need to account for every single species, not solely homo sapiens. And that all life on Earth depends on Earth's resources, mainly water and oxygen.

Unless you're talking of humble cave people (hominins/hominids) who indeed maintained an harmonic relationship with fauna and flora behaving as all living beings do (collecting out-of-the-wild food and hunting preys to eat and survive) while also keeping a balanced reproduction (i.e. not reinlessly procreating), the "modern humans" can't be no polluting. It's the nature of modern humans: modern humans will pollute, whether they live at houses, at apartments or even at "modern caves" (bunkers).

Fire discovery is something to blame for this behavior. There's always someone who'll lit some logs and set fire on wildfire so to "expand their lawn", or there's always someone who'll think "huh, I guess my apartment neighbors need money to exchange things, maybe I could become the leader and build a big polluting factory here to employ them while making industrialized things to sell them, because bartering craftsmanship is a primitive thing we can't accept" (Fun fact: you don't see birds carrying "money" or "goods" across the skies, for example).

Last but not least, I'm no alien nor a jaguar or a tree, so I'm obviously aware of myself. I'm aware of how polluter I am on Earth being a "modern human".

If it didn't become clear, I'm defending for primitive and sustainable ways of life (a return to our hominin origins), ecocentrism (Nature above humans, not humans above Nature), the awareness of how unbridled procreation is dangerous to both the Earth and the humans as well the "right" to live not being a "duty" to live. Again, all "controversial" topics for many people but whatever.