Sentence:  "No matter how rude or <WSD>incivil</WSD> the existing habits of behavior, in other words, "if" the creature was in fact a human being, then he/she was necessarily endowed with a soul and thus with a capacity of understanding at least sufficient to absorb and retain Europe's instruction." 
Meaning of the word marked with <WSD> tags:  Displaying a lack of courtesy; rude, impolite.