The point is that Nora never really was a mother to her children, the maid Ann-Marie took care more of their maternal needs. She only played with them-they were her 'dolls'. Her whole life has been defined by the male figures in her life, first her father, now Torvald. So she leaves to 'find herself' and until she can do that she cannot do or be anything else, including be mother to her children. Ibsen was thus commenting on the role of women in society at the time. There was a second draft of the play which Ibsen was forced to write due to critical reaction to the play, in which Nora does not leave Torvald but stays with him and the kids. It does not really work. Thus the original setup is still used.
As for Hedda Gabler, no she is not evil, just very dangerously bored. But in many ways she is very weak. She is afraid to go after what she wants because she fears scandal. In this way Thea Elvstedt is the stronger character, although she is outwardly demure, because she is not afraid to go after what she wants-leaves husband for Lovborg. In a way, Hedda Gabler's situation becomes entirely of her own doing.