Canonised or no, it was held by a number of well-known and influential early Mormon leaders, not least of which was Apostle Orson Pratt, who derived it from The Book of Doctrine and Covenants, though the Book of Mormon's use of the black skin motif to describe sinfulness on the part of the Lamanites (cf. I Nephi 5:21) probably didn't help matters either. Simply saying that there are black bishops now, doesn't change the fact that blacks were formally kept out of that position, specifically because they were viewed as spiritually secondary, until well into the 1970s. If Mormons were kicked out of Missouri for being abolitionists, then why were there Mormon slave owners in Utah (then Deseret) in the 1850s, including Apostle Charles Rich? Why did Brigham Young tell Horace Greeley that "We consider it of divine institution and not to be abolished until the curse pronounced on Ham shall have been removed from his descendants"? This all after being expelled from Missouri?
Other groups have had their problems with race relations, and I think that is a shame, since Christianity, in and of itself, from what the BIBLE teaches, should be a colour-blind creed. In the early churches, it was, too. I don't have time to look it up and cite it explicitly right now, but Justin Martyr even makes a point of telling his disputant that whereas before, there was division between tribe and ethnicity which led to strife and fighting, in Christ, those differences have disappeared and we can live with each other in peace and worship in unity.
It's a shame that Christianity was misused to justify slavery, especially in the American South. This is the misuse of the sacred to promote the profane, the misuse of the Bible to justify a profitable and "necessary" economic system.
Off the cuff quotes are nice to have, but until the church canonizes it it is just an opinion. I don’t think you want to be responsible for everyone’s opinion in your church either. I don’t let myself get exercised over talks given years ago that were never canonized. Heck, the Cherokee indians had slaves and plantations. I, myself, would rather own a judge than a slave. I think everyone should own a judge. The Clintons seem to own quite a few as they are not pounding big rocks into small rocks despite using government agencies against their opponents like the IRS. I bet there were lots of protestants and catholics that owned slaves and thought it was ok. I think on a sheer wait of numbers the protestants and catholics were bigger into slavery. We were a tiny group back then.