Saas Bhi To Maa Hai

Mothers  are  loved  and  mothers -in-law  hated, mothers  are  considered  loving  and  mothers-in-law  odious, mothers   are  loveable  and  mothers-in-law  condemned,   why?  looking  from the  point  of  view  of  a  mother -in-law  who  loves  her  son , is  she  really  so  bad?