Muslim women having sex with their Milk El Yamin?

In Islam a Muslim woman can have a male slave and she can show her beauty infront of him as stated in Quran سورة النور الٱية 31. Still, there's no Hadith nor an Aya from Quran that denies that she can have sex with him.

And remember, in Islam, Milk El Yamin do not count as wives ot husbands.

The matter is Haram by scholars, but their only reason is a story that happened in the time of Omar.

I searched a lot in this matter and the only two reliable reasons that I found is that a master cannot be submissive to his slave and hence a muslim woman cannot be submissive to her slave in sex. And also, the matter of pregnancy, tho, can a woman have sex with her male slave after menopause?