Unless you are religious and believe in eternal torment after death, death isn't cruel, it's simply an end to life, a permanent return to nonexistence no more or less cruel than having never been born.

Additionally, while they aren't exactly wrong in that going from nonexistence to existence results in an infinite increase in potential for suffering, that holds true for joy/happiness/pleasure.

Imo bringing someone into being is not cruel nor wonderful, not moral nor immoral. It simply is.

Antinatalism is a more deranged branch of eugenics. It's not simply "promoting eugenics" it's a belief that giving birth is the greatest evil one can inflict upon a child and the world at large.

That they'd clearly see us as subhuman isn't surprising given that they at best want our entire species to voluntarily go extinct. Their entire worldview is best summed up as gentle genocide is good.