First let me start off by saying that I am and have been a monogamous brother before and after marriage and do believe that socially there is a double standard. Secondly, that having been said, biologically, the double stand makes mathematical sense, if, and only if, one assume the primary purpose of life is perpetuation of the bloodline.
Mathematically speaking, a promiscuous man can create more offspring in a year's time than can a promiscuous woman. Women are much more valuable in nature than are men. If you want to kill off a people, you will gain more success by killing off the women, than by killing off the men, because men are expendable because of their ability to fertilize many eggs in a short period of time.
Say there are two villages, A and B, of 200 people each, evenly divided between females and males. Now suppose that calamity struck the two villages leaving village "A" with 100 women and one man and village "B" with 100 men and one woman. In 100 years, which village will have multiplied faster? The village with 1 woman, "B", is likely decimated, no matter how promiscuous the lady. Most of the men have died off, as well as the one lady, leaving the village composed of only her children and grand children. However, based upon the virility and promiscuity of the 1 man left in the village "A" with 100 women, the population would have fully recovered is losses and likely have many more than before, with many families.
I believe that biologically, men are predisposed to promiscuity as a species survival mechanism. It does not seem to make sense unless a population is under stress or extinction threat, but it is still our biological programming to ensure or species survival if and when such stress manifest. Strength is the ability to manifest control and male promiscuity today is born from our inability to control our biological instincts, as well as, the behavior being rewarded by females.
I believe that the majority of women are attracted to the "ladies man". If a man got a reputation of being "good in bed", born from promiscuity, many women will covet such a man, whether she acts on it or not. That is not to say that a man is not attracted to a women who is "good in bed", its simply that most men will not want to marry a women who done got good via promiscuity, while many women will [marry] such a man, thinking she can reform him and keep him to herself. In short, women reward promiscuous behavior in men, because if they did not, men would be much less promiscuous. For every buyer there is a seller. If one wants to cut down on the number of sellers of promiscuity, you would need to first cut down the number of buyers of it.
Biologically speaking, there are differences between man and women that should translate to different standards and expectation socially. Men and women are inherently biologically unequal, not intellectually but physically, and attempts to force a social equality will only disrupt nature's intentions and disturb equilibrium. Women are the most valuable and most high in nature. If women simply realized this....and used the power born from that fact for their collective unity and interest, things would be much better for women. However, when women try to use the less valuable and more expendable male behavior as the benchmark that women should strive for equality with, it lowers humanity and causes confusion.