It’s worth mentioning one benefit of slavery that still exists today- facilitating mamzerim getting married.
A mamzer cannot marry a non-mamzer; and if two mamzerim marry each other, their mamzer status gets passed to their children.
How can a mamzer get married and raise a family while eliminating the “mamzerus”?
He marries a shifcha (a female non-Jewish eved who becomes obligated in mitzvos like a regular woman).
His children then are also his avadim. He then frees his children and they become regular yisraelim, minus the mamzer status.
I was speaking with a posek once about slavery and he told me about this.
He mentioned that poskim utilize this lemaase (he mentioned that he knew about Rav Moshe Feinstein and Rav Aharon Kotler giving this guidance, though I don’t know if it is written anywhere).
He said they find non-Jewish women who want to convert to Judaism (for legitimate reasons).
They suggest to them that instead of actually converting, they become a shifcha to the mamzer. (It basically is the same status, since both a female ger and a shifcha need to toivel in a mikvah, and they keep the same halachos.) They just hide her status.
Since slavery is now outlawed in most of the world, it’s hard to do this.
Apparently, nowadays the mamzer and would-be convert travel to places in Africa or Asia where slavery is still legal, allow her to become a shifcha and then let them get married.
Then, even when they return back to the Western world where slavery is not recognized, it still works halachically.
This posek mentioned that some hold it’s enough if they go into the embassy of the African/Asian nation, even though they are still in America, since the foreign country’s laws are applicable in the embassy. (I don’t remember if he mentioned which poskim allow this).
I had heard of this “kuntz” to purify the mamzer when learning in yeshiva. But I never thought it would be applicable today!