Keysar Trad's note on polygamy stems from the 7th century when Mohammed, at the time a penniless warlord, tried to get the warring clans of Bedouins into a meaningful grouping by raiding & conquering nearby clans & carrying off the women & children as slaves. So heavy was the death rate amongst males that many of Mohammed's clan's females were left without a male "protector" without which, in this dry & unforgiving land, they would surely die. Allowing "... up to four wives - provided you could support them" made sense at the time, but Mohammed himself had many more that 4. He had a Jewish wife, another he married at the age of 6 and started sexual relation with at the age of 9, and another where he saw his daughter-in-law semi-clad and liked what he saw. He subsequently made his (step)son divorce her so that he could marry her too! Not a nice man!

Polygamy thus made sense at the time & in the place it started, but unlike much of radical Islam - particularly the radical Wahibism (Saudi version of Islam)- that only came about in the 1740's - it's place in a modern society is questionable.