Humanity!
This was what Lu Li deemed as important. Lu Li believed that the basic factor for being a human being was to have humanity. Without humanity, humans were no longer humans.
Lu Li had adopted a cruel and strict solution. For one thing, what the human warriors had done to the civilian Asmodians and to the female Asmondians were brutal. More importantly, he aspired to preserve the humanity of the human race. He could not let the human race turn violent and vicious or let "the true, the good and the beautiful" qualities slip from a human's mind.
Imagine humans being tortured and abused by Asmodians and the Feather Race. The humans being assaulted, year in and year out. Gradually, the whole human race' nature changed.
They thought torture was natural. Maybe, the whole human race would have a change of heart after dozens of years. Could they already be called humans by then if that was the case?