Why does mama tell Walter he's a disgrace to his fathers memory ?

Mama wants Walter to stand up and take responsibility for his family, she wants him to stop his wife (from getting an abortion) and give her a reason to keep their child.

"Well — son, I’m waiting to hear you say something … (She waits) I’m waiting to hear how you be your father’s son. Be the man he was … (Pause. The silence shouts) Your wife say she going to destroy your child. And I’m waiting to hear you talk like him and say we a people who give children life, not who destroys them—(She rises) I’m waiting to see you stand up and look like your daddy and say we done give up one baby to poverty and that we ain’t going togive up nary another one … I’m waiting."