Couple of points:
In the LDS way of things, "atonement" has to do with forgiveness and "entrance into heaven" - but it would do well to remember that in the LDS way of things there are actually three levels of heaven, and moving up from one level to the next is achieved via obedience in lifestyle or to some ordinance or practice. One does not make it into the Celestial Heaven on Jesus' blood alone. When we discuss "blood atonement" and the LDS church, we are not discussing forgiveness and "going to heaven" in the same context and system that Protestants (and presumably Catholics) do.
Second, the above speech is not an isolated case. There are numerous other sermon examples which could be cited, and several controversial historic examples (the Mountain Meadows Massacre being the most obvious) that could be raised for - or against - the argument that "blood atonement" was taught to, or practiced by, the nineteenth century LDS membership and heirarchy.
Third, the work quoted at the top of the thread, the "Journal Of Discourses", is a multi-volume collection of speeches and sermons given by the various members of the LDS hierarchy that has been published, revised, and republished numerous times, over the course of a century and a half. None of it's contents, although published by the church-owned Deseret Book Company, have not been canonized by the LDS heirarchy, thus no LDS member is morally bound to keep or reject them. What the Journal does, however, is provide volumes of first-hand testimony of how the various LDS latter-day prophets applied the canonical works, in thought and practice, in their personal lives and how they interpreted and exhorted said works to the masses.
Finally, it should be noted that the term "doctrine" probably should be avoided when speaking of "blood atonement" here. "Doctrine" is a buzzword like "canonical" for the LDS, and it means the LDS heirarchy has formally adopted it into whatever they use as a creed or code. "Commonly held belief" would be a better phrase to use in the context of Brigham Young's sermon on "blood atonement".