"The Good Mother" isn't about an evil woman who is punished for her misdeeds. It's about an average, or perhaps slightly better than average, woman who suddenly finds herself victimized in a very painful and very real way.
Why must Anna suffer? Why is there no voice of reason in the courtroom? Because the film makers are condemning female sexuality? Nonsense! The point is that life is not always fair and society not always as just and understanding as it should be.
"The Good Mother" shows us how vulnerable we all are to being judged without compassion, and Avins' nasty attack on the film demonstrates that it is a lesson we need to learn.