Double standard: Women should be virgins at marriage.
The fundamental difference between men and women is that men have an unlimited reproductive potential while women's reproductive potential is very limited. When a man has sex, he is giving away nothing of value. But when a woman has sex, she is potentially giving away a large aspect of her life if she gets pregnant. Today we have birth control to eliminate the practical side of this, but this doesn't change the feelings in us that were produced by evolution before birth control. This is why men still greatly value virginity in women, as can be seen in the cases where women auction off their virginity. But women place no value in the virginity of a man because there is no evolutionary basis for this feeling.
A woman who has sex before marriage is being selfish at the expense of her future husband. A normal husband (who places his emotions and common sense over feminist propaganda) would prefer that his wife be a virgin. Women also seem to be changed by premarital sex and are less able to bond with their husband as explained in Why Sluts Make Bad Wives.
The anthropologist Unwin, in his book "Sex and Culture", studied the isolated tribes of his time to determine what best correlated with level of development. He found one fact that perfectly correlated with level of development. This was female premarital chastity. In all the most developed cultures, women were required to be virgins at marriage. Then he looked at history and he found that in all rising cultures, women were required to be virgins at marriage. And in all cultures where this requirement was lost, the culture went into terminal decline.