As Lolers suggested earlier, I personally think context matters. I also (cautiously) would raise a moral issue. Finally, perhaps most importantly for me, I think, are the implied concepts of power and control.
Probably the most logical comparison is the Haunted Mansion. And full disclosure, it is my favorite ride at MK, and has been since I was a child.
There are clearly some questionable scenes in HM. The hanging in the preshow and the black widow bride come to mind. So, why am I not disgusted by them, the way I am with Pirates?
I’m not sure if I will express these ideas properly but,
1. The women in the auction explicitly had no power or control over their fates. I can think of no example in Haunted Mansion, however, where anyone has lost his or her free will. They still have the ability to affect their outcomes.
2. It is a haunted attraction, so I would expect elements of murder and death. Furthermore, HM is meant to be spooky, while Pirates seems to be intended as humorous. What is funny about a slave auction?
3. Understanding that morality is entirely personal making this point possibly the weakest, I object the most to human trafficking. I can simply find no way to rationalize or justify the buying and selling of human beings.
To raise some much more controversial topics...
I actually object to content in several other rides. For example,
1. I believe both it’s a small world and Jungle Cruise have racist elements. (WDW)
2. I think Country Bears Jamboree is both bigoted and sexist. (WDW)
3. I can’t even look at the murals at the end of Apollo’s Chariot, depicting lions savaging victims in the Roman Coliseum. (BGW)