It is not true that there are "simply more women" in "a general society."
The male-to-female ratio for the entire world population is 1.01 males/female, with 1.06 at birth, still 1.06 for those under 15, 1.03 for those between 15 and 64, and 0.79 for those over 65.
So, for the world there are more men than women in every age group except old people well past their childbearing years. Also I would say, well past wanting to get married if they haven’t already, or marry again if they have.
It is true that there are about 4,303,361 "extra women" in the United States.
The male-to-female ratio for the population of the United States is .97 males/female, with 1.05 at birth, still 1.05 for those under 15, 1.02 for those between 15 and 54, and 0.82 for those over 54; 51 is the average age for menopause in American women.
All of the "extra women" are 54 years or older. So, if 2 or 3 million polygynists would commit to marrying all the extra women over age 54 I'm sure that would make them happy.
Please use statistics wisely and correctly.
I know that accepting this information as fact will seriously undermine your mathematical defense of polygyny. However, perhaps this just means that you will have to focus on other aspects besides statistics.
For instance, polygyny could be posited as the demographic counterpart to male homosexuality, and perhaps you could argue that as long as adults are free to make these choices, both lifestyles are acceptable. (Although you might have a hard time putting this past female homosexuals.)
Or, you could argue from a biological standpoint, where as with lions, the females mate only with the most desirable male and thus strengthen the gene pool because the other males are unable to pass on their less-desirable genetic information.
Or, you could say that polygyny is perfectly acceptable from a moral standpoint as long as it is used wisely. For example, it can be traditionally recognized as a useful means to populate or repopulate an area when this has to be done quickly, and then the practice can cease until it needs to be used again.
Sources: CIA World Factbook and US Census Bureau.
Comments
As for any survival arguments let's not forget that humans have not only won the evolutionary battle (at least for now) but have beaten the game so badly that our only real enemy is us.