I think the problem that you are having is in thinking that once a man becomes a prophet he becomes infallible. I sthat what the issue is here?
No I do not think that. However, based on what the founding prophet of the LDS Church taught this
KFD:
In the first place, I wish to go back to the beginning--to the Creation. That is the starting point if we are to be fully acquainted with the mind, the purposes, and the decrees of the great Elohim who sits in yonder heavens. We must have an understanding of God himself in the beginning. If we start right, it is easy to go right all the time; but if we start wrong, it is a hard matter to get right.
There are very few beings in the world who understand rightly the character of God. They do not comprehend that which is past or that which is to come; and consequently they know but little above the brute beast. If a man learns nothing more than to eat, drink, and sleep and does not comprehend any of the designs of God, he is equal only to the beast, who comprehends the same things: it eats, drinks, sleeps, and knows nothing more; yet it knows as much as we, unless we are able to comprehend by the inspiration of Almighty God.
I want to go back to the beginning and so lift your minds into a loftier sphere, a more exalted understanding than what the human mind generally understands. I want to ask this congregation, every man, woman and child, to answer the question in his own heart what kind of a being God is. What kind of a being is God? Does any man or woman know? Have any of you seen him, heard him, communed with him? Here is the question, perhaps, that will from this time forth occupy your attention. The apostle [John] says, "This is life eternal"--to know God and Jesus Christ, whom he has sent. If any man, not knowing what kind of a being God is, inquires to know if the declaration of the apostle is true--and searches diligently his own heart--he will admit that he has not eternal life; for there can be no eternal life on any other principle.
Thus knowing who God is seems of utmose important and if the second prophet of the LDS Church got who God it wrong it seems that eternal life is hanging in the balance.
We are expected to follow his direction and advice, but that does not mean that a prophet is suddenly Jesus Christ incarnate, never taking a backward step.
I never said that and you are building a straw man.
By the way as an aside, we are often told the prophet cannot lead the Church astray, and to follow the brethren. This seems to imply a defacto infallibility that in fact leaders in the early 20th century, particularly Pres. Clark, discouraged.
So, anyway, no I do not believe in infallible prophets but I do believe there are fundamentals that are hugely important to get right and this is one of them.
The scriptures are rife with prophets who messed up and had to straighten things out. Samson is a prime example. David and Solomon as well. Because these men messed up, does that mean that their stories are not good to study and learn from?
David and Solomon were not prophets in this sense and LDS scriptures state that David lost his exaltation because of what he did.
Brigham was a great man, and got this one issue wrong, if he led men astray with this doctrine, he will be held accountable and probably caused to suffer for a season for this mistep.
This really still begs the question.
But he, like Solomon, brought salvation to many and accomplished his mission in this life for which he had been set apart in the pre-existence. A mistep towards the end pales in comparison to all that he accomplished.
If he taught people to worship a false God he broke one of the Ten Commandments.
Brigham got it wrong on that issue. The vast majority of prophets from that time concur on this. I stand with those who have been called to lead in my time.
Well I agree with you that on this point that yes, Brigham got it wrong.