Second, although I expect prophets to reveal the will of God from time to time, I don't expect or require them to absolutely transcend their time and culture. There's no evidence, in any event, that anybody has ever managed to pull that off. On racial matters, Brigham Young reflected his time and culture more than I, comfortably ensconced in the more racially sensitive twenty-first century, would have liked. (I have no doubt that twenty-second century people, if they ever think of us, will be appalled by some of the things that we take for granted as right and good.)
But here is the problem with this. If Brigham the prophet was just a product of his times and the ideas about race he espoused were erroneous why did not God correct him? Why let him be a product of his culture. It seems that God had no problem revealing the practice of polygamy and that was certainly outside the cultural norm of the 19th century. Much more so than bucking racist ideas of the time.