Actually, I agree with you. The Manifesto IS doctrine. The question is whether or not it comes from God, or is the action of men who wanted to become more acceptable to the World.
You are right, it is an "Official Declaration." That doesn't make it a revelation, nor scripture. Yes, it was used to end the practice of plural
marriage. However, after its publication, President Woodruff promoted the continued practice of plural
marriage, as did Lorenzo Snow and Joseph F. Smith. President Smith actually entered into an additional
marriage after the Manifesto.
But this leads into a much more important, more interesting discussion.
If the words of the Prophets, especially at conference time, are to be considered scripture, then the words and actions of Heber J. Grant and all subsequent Prophets have been clearly and unmistakably in opposition to previous scripture. And, it wasn't until AFTER the Manifesto that we first hear about the idea that the Prophets can not be led astray, or that they can't lead the Church astray. It wasn't until AFTER the Manifesto that Prophets could contradict former Prophets.
So, let's look at a couple of facts.
The last Prophet to claim a clear, unmistakable "vision" revelation was Joseph F. Smith. President Grant, following President Smith in office, publicly stated that the heavens were as brass above his head - clarifying that he was not receiving revelation at that time.
The last Prophet to have made ANY sort of claim as to meeting the Saviour personally, was President Snow. He had spent HOURS in the Holy of Holies, praying for a manifestation of some sort that his work and ministry was acceptable to the Lord. However, he never received that acceptance. Of course, the Holy of Holies is considered the "official" place of revelation, the place where the President of the Church is clearly and unmistakably acting in his leadership role as Prophet.
When President Snow left the Holy of Holies, Jesus Christ appeared before him. Why did Jesus wait until AFTER he left the Holy of Holies? Why did President Snow NOT publish to the Church what the Saviour said to him? Could it be that Jesus very clearly and fully accepted the work and efforts of the
man - Lorenzo Snow - but wasn't so happy with the work and efforts of the Church?
Why was the "Manifesto" not enforced until the 1930's, after President Grant was firmly established, and all polygamist Apostles had died? Why have NONE of the Prophets who have NOT lived the Principle while in office reported a clear and unmistakable visionary revelation? Could it be that the Manifesto is the visible symptom of something not right? After all, the Manifesto, and all that has come from it is in direct contradiction with teachings of Joseph Smith, Brigham Young, John Taylor, Wilford Woodruff, Lorenzo Snow, and Joseph F. Smith. Every one of them said, more than once, that if the Church gave up the Principle of Celestial Plural
Marriage, it would be in apostasy, and would become just like the World.
One more quick point, then I will retreat to silence again.
It was not a revelation. There is no claim, anywhere, that Wilford Woodruff said it was a revelation. He said that it came AFTER he received a revelation. That revelation he DID receive showed what would happen to the Church. What he never explained was whether what he saw in the vision was because of the Principle, or if it was because the Saints had already apostatized in rejecting the Principle, and refused to allow the Lord to fight the battle for them.
Disclaimer: I am not a fundamentalist. Think what you may, but I am not.