"My Mother" is a study of a mother's quest for destruction and its influence on her son. It is not a moralistic fable that describes the pitfalls of a profligate life. This kind of purist concept of human sexuality is completely opposite to the philosphy Bataille writes about in this and other texts.
In "My Mother", the liberal lifestyle and sexual openness of the characters comes not from of a slow, fatalistic slumping towards the gutter, but from a quest for an intense experience, especially sexual experience. This attitude is seen when the mother writes to her son "I have absolutely no interest in this world where they scratch about, patiently waiting for death to enlighten them. As for me, it is the wind of death that sustains the life in me."
Then the son realizes that in his solitude, he would be hardened and shocked when he thinks of his mother's crime made her closer to God. The comparison of base sensuality with being divine, and the constant reference to taboos in this story are combined with an ultimate moral ambiguity. These are demonstrated in the other two stories as well.
Bataille's writing is excellent if you can take its pornographic imagery and blasphemous language. His stories and essays are critical of religion, morality and social norms. This stuff is not just well-written erotica: it is profound and provocative philosophy.