charliehall: A lot depends on where they were living. One rov in New Orleans (R’ Illowy? The name sounds familiar) gave a whole drasha about this- but then again, he lived in New Orleans.
R’ Morais lived in Philadelphia.
Your location can influence the way you think, especially during a time of war.
Were there any rabbanim who lived in the South who protested slavery? Probably not, but it’s difficult to expect them to have said anything in an environment like the antebellum South, which obviously PERPETRATED this kind of treatment and weren’t kind to those who protested it.