It should be noted that in many Muslim societies today the practice of polygamy is rare since the gap between the numbers of both sexes is not huge. One can, safely, say that the rate of polygamous marriages in the Muslim world is much less than the rate of extramarital affairs in the West. In other words, men in the Muslim world today are far more strictly monogamous than men in the Western world. If present-day Christianity cannot do so, it is to its own detriment. Islam has permitted polygamy as a solution to social ills and has allowed a certain degree of latitude to human nature but only within the strictly defined framework of the law.
Christian countries make a great show of monogamy, but actually they practice polygamy.
No one is unaware of the part mistresses play in Western society. In this respect Islam is a fundamentally honest religion, and permits a Muslim to marry a second wife if he must, but strictly forbids all clandestine amatory associations in order to safeguard the moral probity of the community. It is of interest to note that many, non-Muslim as well as Muslim, countries in the world today have outlawed polygamy. Taking a second wife, even with the free consent of the first wife, is a violation of the law. It is one of the unfathomable paradoxes of our modern 'civilised' world.