They don't know any particular specifics. Our understanding of human organization during the late pleistocene and early Holocene is poor, bordering on non-exist

They don't know any particular specifics. Our understanding of human organization during the late pleistocene and early Holocene is poor, bordering on non-existent. However, I don't find it particularly hard to imagine humans as a major factor, even if I have some doubts about this particular argument. First, you have to understand that about the late quaternary extinctions, we know not all quaternary extinctions were anthropogenic. Ecosystems were experiencing a lot of different stressors around that time, and by the time extinction actually happens there may have been only small populations left for centuries or millennia. Ecological resilience is also a bit of a funny thing. You might think that you make 10 species extinct has 10x more impact than just 1 extinction, but there isn't a linear relationship. In many ecosystems, there's very little impact from most local extinctions as the graph thins out until all the systemic resilience is gone and the whole thing suddenly collapses into a new state. Did that proximate cause(s) of the last extinction cause the rapid shift? Fantastically deadly hunters like humans that are specialized to megafaunal hunting being able to push the most vulnerable and stressed parts of the ecosystem over the edge isn't an obviously absurd argument to me.