The quote takes a position of non-interference with the process with naturally occurring selection pressures on animals. When the discussion involves humans a

The quote takes a position of non-interference with the process with naturally occurring selection pressures on animals. When the discussion involves humans and eugenics, it's the complete opposite and revolves around substituting a human chosen selection criteria with all the possible inclusion of criteria with very limited knowledge of the long term impacts, a minimal knowledge of short term impacts, and often biases driven by hubris and racism assessing the benefits vs the unknowns. That's why it's controversial.