As the dispute in John 8 intensifies, Jesus' opponents answer, 'Say we not well that thou art a Samaritan, and hast a devil?' The words are not neutral attempts at biography or diagnosis.
They are polemical accusations intended to dishonor Jesus and undermine his authority.
Jews and Samaritans were divided by long-standing disputes over sacred geography, ancestry, and worship. In a hostile Jerusalem debate, labeling Jesus a Samaritan could mark him as religiously suspect and outside accepted communal boundaries. Accusations of demonic influence similarly appear in ancient religious controversy as ways of explaining or discrediting extraordinary claims and behavior.
Jesus explicitly denies having a demon but does not separately answer the Samaritan insult.
Recognizing the rhetoric prevents the verse from being treated as reliable evidence that Jesus was thought ethnically Samaritan. The speakers are insulting an opponent.
John also frames the exchange through honor: Jesus says he honors his Father while his opponents dishonor him, leaving final judgment and vindication to God.