the one relatively non-religiously rooted point attempted is that absence of polygamy results in single women. this assumes that women significantly outnumber men. that is not true, the proportion is pretty much the same and in certain places there are more men than women. infact if there was a significant degree of polygamy, the result would be single men.
Slightly more women than men is due to the fact that women enjoy better longevity .. now these advocates of polygamy don't go around marrying these 80+ women do they.. they are more interested in damsels in 20's..
in nutshell it's lame justification by those people who want to make merry at the expense of women folks..