I think the only way that a boy's sexual development could be negatively impacted by his mother would be if she acted in an overtly sexual way toward him.
There are plenty of ways a mother can shame the son. If sex is taboo in the family, then any teasing of the boy in a way that is not intended to be complimentary or boosting his ego can be harmful. He will be teased for something he has already been told is shameful. Your assumption is wrong.
