> the kings of a kingdom built on slavery.
You cannot put that as a reason to keep the artifacts in the UK, of all places.
Why not? The UK had being making huge military efforts to suppress the slave trade for ninety years at the time it seized the Bronzes: https://en.wikipedia.org/wiki/West_Africa_Squadron
Didn't the movement to stop slavery come from the UK? After that happened the African region refused to stop because it made them rich so England had to invade and created the Ivory Coast? England has a lot of credibility.
The idea of reparations has come up. Should the US be paying or the African countries who profited and kept it going for another 100 years.