(Personal opinion with no intent to argue or pursuade) I think you are asking the wrong optimisation question. Indeed species have been going extinct forever an

(Personal opinion with no intent to argue or pursuade) I think you are asking the wrong optimisation question. Indeed species have been going extinct forever and differing rates. I think what we should be optimizing for is quality. I remember as a kid growing up in SE Utah just being overwhelmed with insect, reptile, amphibian, and small game wildlife in the area. You didn't look for it, it was just around. I visit frequently and have been amazed at the decline I've witnessed in just 30 years. So few of everything. Now we search for lizards and horned toads. I hardly ever see butterflies and bees. It's [not] wild. I also just drove in August from SE Idaho to Tacoma. Mostly through Montana and Idaho. I didn't have to clean my windshield once the entire trip, there and back. I remember driving as a teenager it seemed like I always had to clean my windshield, even driving on I-15 from Salt Lake city to SE Idaho. Cleaning dead bugs off my windshield is something I don't need to do anymore. I haven't done it for a long time. We could model our existence in a way to just optmize for our species existence. Humans have been running species into existence for a long time in order to populate. I think we should optimize the other way though. I think we would if we assumed that our mentally advanced status assumed a stewardship-like responsibility. Instead we take and take and take. I've been guilty as anyone, but have tried to be more mindful as I've gotten older and limit my consumption, and make sacrifices to do so where I see nobody else in my immediate sphere doing the same. I do that because I liked having nature be outside my doorstep. I don't think there is an asumption that there was or is an optimal number of species, I think it is just that some people have seen a tranformation that they don't like.