This line of reasoning could lead to the unfortunate conclusion that late-term abortions, that threaten the mother's life, are immoral. Abortion ultimately comes down to the reality that the mother does not want the child. From a social, legal point of view child neglect and adoption policies are important factors. The alternatives that the mother faces are relevant. I don't see what the popularity of an action has to do with its morality.
Most people are superstitious, yet it is detrimental to our well-being, ie.
The actual discussion of adultery demonstrates the moral conflicts caused by mixing evolutionary 'goals', social acceptance, personal feelings, and rational ethics. From all points of view offered, adultery seems to be OK provided that you don't get caught. From a social point of view there is the risk of ostracization. In the end, the golden rule is invoked as a test for morality. She may have no desire to cheat.