“We were not born of sexual immorality”
We are not illegitimate children… Our only Father is God Himself. (John 8:41 BSB)
What it sounds like today
A neutral family identification.
The cultural key
Two barbs hide in the wording. Matthew's version says 'the carpenter's son'; Mark's crowd calls Jesus 'the carpenter' outright, pinning him to the workbench. Sharper still is 'son of Mary': men were normally identified by their father even long after the father's death. Naming a grown man by his mother in public was irregular and, many scholars judge, insinuating, a whispered question about his legitimacy that may echo again in John 8:41 ('We were not born of sexual immorality'). Many readers hear in this retort the same whispered slur that 'son of Mary' carries in Mark: the emphatic 'we were not born of immorality' insinuates that someone present was. If so, the rumor about Jesus' birth was alive in his lifetime and was being used against him to his face.
Recovered meaning
The hometown does not just doubt Jesus; it reaches for the oldest slur available. Mark notes he could do no mighty work there: contempt, not distance, is the great insulator against him.