Based on observation of the labor market, it seems as if women have a tendency to drop work and spend time taking care of the children, cleaning the house, etc.
If women have a bias towards these traditional tasks, their work will suffer. This can be seen in statistics showing that women get paid less than men. However, it's worse then that. Because women are more likely to quit, firms will discriminate against them because they are worried about whether the woman is dedicated to the job.
For example, suppose I have a man and woman applying for a job. Both we'll assume are equal in everything like experience and education. But the man simply by being a man is less likely to become a housewife and quit to have babies. Therefore, for the sake of avoiding the inconvenience of having to hire maternity replacements, firms will discriminate against women.
Discriminating against women is fair if women as a whole choose to become submissive housewives. By choosing to be housewives, women voluntarily sacrifice higher wages. But what doesn't sit well with me is the effect this discrimination is having on innocent women who don't want to live traditionally. What about the females who are dedicated to their careers? Unfortunately, employers cannot ask a woman to sign a contract forbidding her from having a baby (because of anti-discrimination laws). Therefore, the employer cannot distinguish between career woman and housewife woman. What happens then is that employers will discriminate against all women. The selfishness of the housewife has encouraged employer sexism and has dragged down the innocent career woman in the process.