Adam Clarke on Esther 1:16

Vashti - hath not done wrong to the king only - This reasoning or arguing was inconsequent and false. Vashti had not generally disobeyed the king, therefore she could be no precedent for the general conduct of the Persian women. She disobeyed only in one particular; and this, to serve a purpose, Memucan draws into a general consequence; and the rest came to the conclusion which he drew, being either too drunk to be able to discern right from wrong, or too intent on reducing the women to a state of vassalage, to neglect the present favorable opportunity.