There is a common misconception about the position Islam takes on Slavery and Polygamy.
Slavery is mentioned in at least twenty-nine verses of the Quran, most of these are revealed in Medina and refer to the status of slaves. The verses are largely restricted to manumission (freeing of slaves) and marital relations. The Quranic references to slavery mainly contain broad and general propositions of an ethical nature rather than specific legal formulations.
The Quran uses "slavery" in the past-tense, thus an indication only to those individuals who were already enslaved at the time of revelation. This meant that slavery was never compatible with the commandments of the Quran and was in fact outlawed by Quranic Law.
The Quran recognized the practice of inequality between master and slave and the norms at that time about the rights of the former over the latter. But the Quran stated that from a spiritual perspective, "the slave has the same value as the free man, and the same eternity is in store for his soul.
The Quran urged kindness to the slave and recommended their liberation by purchase or manumission. The freeing of slaves is recommended both for the expiation of sins and as an act of simple benevolence. It exhorted masters to allow slaves to earn or purchase their own freedom.
The Quran, however, did not consider slaves to be mere chattel; their humanity was directly addressed in references to their beliefs, their desire for freedom and their feelings about being forced into prostitution and forced labor. In one case, the Quran referred to master and slave with the same word, rajul (man). Later interpreters presumed slaves to be spiritual equals of free Muslims. For example, verse 4:25 urged believers to marry believing maids that your right hands owned and then stated: "The one of you is as the other," which the Jalaalayn (exegeses of the Quran by Jalal ad-Din Mahalli and Jalal ad-Din as-Suyuti) interpreted as "You and they are equal in faith, so do not refrain from marrying them." The human aspect of slaves was further reinforced by reference to them as members of the private household along with wives and children.
The purpose was not to promote or sustain slavery but to eliminate it completely. It took Muslims some 1400 years to realize this intent and now slavery is completely banned in all countries including the Muslim majority countries.
On the issue of having multiple wives, there is only one verse of the Quran in which polygamy is mentioned. "And if you have reason to fear that you might not act equitably towards orphans, then marry from among [other] women such as are lawful to you - [even] two, or three, or four: but if you have reason to fear that you might not be able to treat them with equal fairness, then [only] one - or [from among] those whom you rightfully possess. This will make it more likely that you will not deviate from the right course." (Surah an Nisaa - Women 4:3).
This reference to polygamy, or having multiple wives, was discussed as a response to a specific social situation of war-torn society in seventh-century tribal Arabia, The purpose was not on multiplicity of wives but on social justice in the context of the social structures prevalent at that time.
Polygamy was meant to be viewed as a component of justice in the treatment of widows and it was mainly to offer fair care to orphans. Its functional purpose was to allow widows and orphans to be taken care of in a social structure in which women usually did not have independent means of financial support and orphans did not have any legal status to exist as responsible beings.
But the text was clear that polygamy was only permissible if all wives were treated justly. But the Quran warned that it would not be possible for a husband to treat all of his wives fairly. This effectively eliminated the possibility of polygamy tin practical terms.
If we look at the verse in detail we find that it talks of dealing justly with orphans, and is directed towards their male guardians who might assume their guardianship. Marriage to female orphans was only suggested only if the guardian feared that he would not be able to carry out his duties honestly. It was personal and ethical issue. The assumption was that marriage to the orphan would give him a greater stake in managing the financial responsibility towards her. It did not say that all male guardians must marry their female wards.
The verse also emphasized justice towards the wives. As the Quran said: "And it will not be within your power to treat your wives with equal fairness, however much you may desire it; and so, do not allow yourselves to incline towards one to the exclusion of the other, leaving her in a state, as it were, of having and not having a husband. But if you put things to rights and are conscious of Him-behold, God is indeed much-forgiving, a dispenser of grace" (Surah an Nisaa- Women 4:129)
Thus monogamy is the rule for marriages and polygamy is not relevant in our world today because there are alternative venues available to secure justice.
The irony is in our inability to look at the Quranic verses in a consistent and relevant manner. While, practicing slavery for almost 1400 years legally, all scholars have declared it illegal and un-Islamic today but on polygamy, despite the Quranic emphasis on equality and justice and having one wife, many scholars still support and find justification for it.
Divine guidance must not be used to serve the interests of a specific group, gender or race.