Too many people simply expect too much from prophets. If we reject our modern prophets because they were spectacularly wrong on certain things, while being incredibly inspired on others, then there have been no legitimate prophets in the history of the world. On the other hand, if we expect our prophets to be infallible - to speak the direct word of God in all matters every time they speak, then there have been no legitimate prophets in the history of the world. If that is our standard, God has never spoken to mankind - and, by extension, there might as well not be a God. That’s not hyperbole; if prophets have to be infallible, even on “important stuff”, there ain’t no such thing as prophets.
Perhaps the best example of this, in my opinion, is the Priesthood ban. The central messages from the 1978 revelation, and from Elder McConkie's subsequent repudiation of the previous justifications, appear to have been twofold:
1) ALL worthy male members now were entitled to the priesthood.
2) God wanted His prophets and apostles to stop speculating about things that had not been revealed. McConkie’s statement at BYU was instructive for that very reason. He said, essentially, that the problem arose from prophets talking about things with only a limited light and understanding. That leads directly now to “I don’t know” when an apostle or prophet has not received personal revelation concerning something.
I probably should follow that advice more often, but I don’t speak for the Church. Apostles and Prophets do. (Look at Elder Benson vs. Pres. Benson. The difference between what he said prior to becoming President and afterward is striking.) Hence, apostles have been much more reticent to give personal opinions lately when asked about things where there has been no direct revelation.
If we criticize Brigham Young and Bruce R. McConkie for their incorrect speculation, then criticize Pres. Hinckley and current leaders for their unwillingness to speculate, we have created an un-winnable situation. They are damned if they do and damned if they don’t.“I don’t know” is a reasonable answer - and we shouldn't try to have it both ways.