If you fear that you shall not be able to deal justly with the orphans, marry women of your choice
The purpose of this sentence is already covered in the linked duplicate:
It was revealed regarding a person who has an orphan girl under his guardianship and wishes to marry the orphan to himself. This is a 'conflict of interest' and can lead to injustice. That is because the groom's interest is to lessen the Mahr while the bride's interest is to have more of it. The guardian of the bride is supposed to look after her interest, but now the guardian is also the groom, so he will become biased in his own favor. Hence this verse tells those guardians to not marry their wards and rather to marry any other women to avoid injustice. The other women would have a separate guardian or father who would look after her interests while formulating the marriage contract - as narrated by Aisha.
Or it was mentioned because people feared being oppressive to orphans but did not fear being oppressive to their wives and married numerous women and neglected their rights. Hence this verse means:
If you fear that you shall not be able to deal justly with the orphans (then also fear being unjust to your wives and hence) marry women of your choice, two or three or four; (but do not marry more than four as it would be injustice) but if you fear that you shall not be able to deal justly (even with even two, three or four wives) then marry only one
In either case this sentence does not obligate or encourage us to marry orphans in the first place. Also it is not a condition for marrying other women. Rather marrying other women (one or more to a maximum of four) is permissible regardless of the orphans.
As an example to illustrate this, consider the following verses:
وإن كان ذو عسرة فنظرة إلى ميسرة وأن تصدقوا خير لكم إن كنتم تعلمون
And if someone is in hardship, then [let there be] postponement until [a time of] ease.
— Quran 2:280
Does this mean that postponing a debt is haram unless the borrower is in hardship? No, rather it is unconditionally permissible for the lender to postpone a debt out of generosity.
وإن كنتم على سفر ولم تجدوا كاتبا فرهان مقبوضة
And if you are on a journey and cannot find a scribe, then a security deposit [should be] taken.
— Quran 2:283
Does this mean that taking a security deposit is forbidden unless you are on a journey? No, rather it is unconditionally permissible for the borrower and lender to agree upon a security deposit.
In the same way "If you fear that you shall not be able to deal justly with the orphans" is not a condition but just describes one situation in which you would do this. And if you argue that it is a condition then it should also be a condition for monogamy since the verse says:
If you fear that you shall not be able to deal justly with the orphans, marry women of your choice ... if you fear that you shall not be able to deal justly then only one ...
So are you claiming that even monogamy is unlawful unless it is with an orphan? Such a claim is ridiculous and can easily be refuted by numerous examples, including from the Quran:
قال إني أريد أن أنكحك إحدى ابنتي هاتين
He said, "Indeed, I wish to wed you one of these, my two daughters..."
— Quran 28:27
قال هؤلاء بناتي إن كنتم فاعلين
[Lot] said, "These are my daughters - if you would be doers [of lawful marriage]."
— Quran 15:71
Are you instead claiming that monogamy is permissible with a non-orphan but only polygamy is forbidden? If so you need to provide evidence for this distinction. Verse 4:3 certainly does not make such a distinction.
Polygamy with non-orphans is permissible. The Quran clearly says that it is halal to marry any non-mahram woman:
وأحل لكم ما وراء ذلكم
And lawful to you are [all others] beyond these
— Quran 4:24
Non-orphans are included in the permission granted by this verse as they are 'beyond these' (i.e. they are not present in the list of mahrams in verse 4:22-24). Non-orphans remain included in this permission regardless of whether the groom is single or already married - there is simply no evidence which excludes them.
Polygamy was practiced by (at least) Abraham, Jacob, David and Solomon عليه السلام among the prophets. It was also practiced by Prophet Muhammad ﷺ.
There is no indication that their multiple wives were orphans, rather at least Aisha, Hafsa and Umm Habiba were not orphans - yet the Prophet was married to them simultaneously.
The Sahaba also practiced polygamy, and the pre-Islamic Arabs and Jews also practiced polygamy - no verse in the Quran or Hadith limits this practice other than prescribing justice and putting a limitation on the maximum number of wives:
أن رسول الله صلى الله عليه وسلم قال لرجل من ثقيف أسلم وعنده عشر نسوة حين أسلم الثقفي أمسك منهن أربعا وفارق سائرهن
The Messenger of Allah, may Allah bless him and grant him peace, said to a man from Thaqif who had ten wives when he became muslim, 'Take four and separate from the rest.'
— Muwatta Malik
أسلمت وعندي ثمان نسوة فذكرت ذلك للنبي صلى الله عليه وسلم فقال النبي صلى الله عليه وسلم اختر منهن أربعا
Al-Harith ibn Qays al-Asadi: I embraced Islam while I had eight wives. So I mentioned it to the Prophet (ﷺ).
The Prophet (ﷺ) said: "Select four of them."
— Abu Dawud
If the claim in the question was true, then the Prophet ﷺ should have told these people to divorce all the non-orphans and to only keep the orphans as wives. This is clearly not the case.
Hence, verse 4:3 consists of two distinct teachings:
- If you fear being unjust to orphans under your guardianship, then marry any other women.
- In any cases a male can marry up to four women, however if he fears being unjust then he should marry only one woman, or he should not marry at all but rather satisfy his needs with his slave concubines.