On the rise of serfdom in the 9th and 10th centuries. Honorius Augustodunensis (Who was born in the 11th Century) made an allegorical argument pointing out how medieval Europe was divided into three classes, one of them being "Servi" or the serfs of serfdom and linked them to Ham and the so called "Curse of Ham"...which was odd because once again, that was Canaan. By the 1300's this idea became popular...a rather theologically uneducated idea but an idea nonetheless.
Honoré d'Autaun was more of a XIIth century man, which does have its importance : it'sto be tied with the Renaissance of the XIIth century and the connection with eastern sources : we're rather in the period where it (slowly, indeed) began to disappear (interestingly, at first on clerical grounds, such as
salvetats)
You'll note that Honoriu's division is, as you said, weird : serfs came from Harm, knights from Japhet and the others from Shem. It's probably because the explanation was not racial or quasi-racial as it was with the Curse of Ham narrative (from which I mean not the disivion of the world overall along Noah's descendence, but the specific quasi-racial or racial essentiallisation of a people identified with Ham), but rather spiritual : serves as Ham's people is likely a didactic device, on par with his other works.
that Christianity used the Curse of Ham to initiate the modern notion of race and racism when it wasn't such interpretation didn't come about when Catholicism spread through most of Europe
Certainly : Ham was rather used on a literary and didactic sense : while serves tended to be described as a low form of humanity, especially in England, eastern Germany, and these specific regions (it's still a thing in France or Western Germany but far less essentializing, and overall disappearing when serfdom turned into a semi-free pesantry, or virtually free eventually). And even there, the comparison between model and reality shows a wide gap : social and familial mobility were too great to really have a practical applicability.
The medieval distinction is essentially the good ol' three orders of society, a model which was already crumbling by the time it was written down in the XIth century, and was continuously adapted, ending with the XVIth century idea that everyone should pass trough the three groups in his life.
Initially, Ham as progenitor of blacks was simply an explanation for their skin color (something many Europeans simply weren't used to).
You did have this explanation appearing in the XIIth from Eastern Med, tough : while fairly tied with late medieval slavery in Spain and Italy it, so to speak, preserved a quasi-racial explanation with slavery : I think we agree that, as Caribbean slavery was in direct continuation of late Medieval practices (including the dominance of Europeans on servile trade roads from the XVth onwards, it played an important role into the essentiallisation of the idea. It's no wonder that Spanish ethnical/identitarian vision of society and the "other" included racial basis , would it be about slavery or heresy/Judaism, IMO.
The reason why they needed to add on to the Curse of Ham was because by the 1500's it was understood that Christians ought not to enslave Christians.
Southern European societies didn't really have a problem with that even in the XVIth century : servile polls went as far as Albania and Greece on this regard, the Duchy of Athens in the XIVth, then Turks being the prime market. Mostly East Europeans such as Albanians, Serbs or Bulgarians (Greek slavery is mentioned but it's more of a XIVth thing than XVth) all of them Christians. And of course, you have Aragonese slave-hunting in Balkanic peninsula.
I widely agree that these captives were generally integrated into southern european societies eventually, as clientelized groups, which is more than what African slaves could expect (even if not unheard of). But what was understood was less that they shouldn't be enslaved, rather that they should be enslaved...kindly.
I don't think we disagree, just that we weren't understanding each other.
Probably, on most grounds.