Salamun alaikum,
Try to find out what is a "legal exception/exemption".
General Rule Exception
Forbidden to eat -> Can eat flesh of swine
flesh of swine (Emergency)
(2:173) (2:173)
Cannot kill -> Can kill
a person (War)
(22.39)
One wife -> Multiple wives
(33:50) (orphans)
(4:3)
and so on..
Terrible comparison. Eating pork and killing a person/existence is "haram"/inviolable/forbidden - and one can only do these in certain conditions. Marrying more than one wife is nowhere stated as being inviolable/forbidden. In fact it is talked about as something that happens, e.g. 4:23.
Also, the exception in 33:50 that does not apply to al mu'mineen is: if a mu'minatan woman gave herself to the prophet - by forfeiting the dowry - the prophet may marry her without a dowry, if he so wishes. That is all. Notice that only "mu'minatan woman who gives herself to the prophet" - i.e. without a dowry - has a "wa" and the other categories of people do not. Then right after that it says that this is not for al mu'mineen.
The exception that prevents polygamy is given directly in 4:3, namely: if you men have reason to fear that you might not be able to treat them with equal fairness, then one or "ma malakat aymanakum."
It is also stated in Sura (4:129):
"..you will never be able to be equal between wives, even if you should strive.." (4:129)
Basically it means it will never be just to marry more than one and it is against Islam, UNLESS it can bring justice to the orphan and wives (lesser). It will bring more justice if they are able to benefit the orphan and at the same time, are able to be equal between their wives. It is only in this situation Allah made it lawful to marry more than one woman.
Peace.
Common distortion, short-sightedness and twisting of the almighty god's words to appease certain "shayateen" - rebellious desires and people - in this case feminists. It is noteworthy that those who argue about plural forms used to somehow discredit polygamy (earlier in this thread) do not step in here. Let us read in context:
4:128 If one woman has experienced from her one husband ill-treatment/uprising or desertion, then it is not undignified for the two to reconcile between themselves; and reconciliation is better. (Greed is ever-present in human consciousness. If you do good and are prudent, then the god is expert over what you do.)
Clearly this is about being unfair to a wife, not about discouraging polygamy!
4:129 (You (male plural) will not be able to be fair regarding the women even if you make every effort.) So do not sway (male plural) too greatly and leave her as one hanging in a void. If you reconcile and are prudent... god is forgiver, mercy-giver.
People fail to realize that asides are used in the reading. The clause "you
(male plural) will not be able to be fair regarding the women even if you make every effort" is an aside and a fact given by the god, while "so do not sway too greatly and leave her as one hanging in a void. If you reconcile and are prudent... god is forgiver, mercy-giver." is a continuation of the problem and reconciliation in 4:128. "Do not sway" is in male plural form, showing that this - as are all commandments regarding relations between men and women - is addressed to men in general when dealing with one/each wife.
Together, in context and understood properly, it reads as follows (with main clauses bolded for clarity):
If one woman has experienced from her husband ill-treatment/uprising or desertion, then it is not undignified for the two to reconcile between themselves; and reconciliation is better. (Greed is ever-present in human consciousness. If you do good and are prudent, then the god is expert over what you do. You men will not be able to be fair regarding the women even if you make every effort.)
So do not sway too greatly and leave her as one hanging in a void. If you reconcile and are prudent... god is forgiver, mercy-giver.