What never ceases to amaze me about John Dehlin is that when he asks questions, they are of the level of a person who has heard things for the first time, but he acts as though he is the one who made the actual discovery. And besides, we know that John is not really interested in getting the question answered or even in asking questions; he just makes statements to provoke his legions of followers into thinking they were justified in leaving the Church. That, or he wants myself and fellow bloggers and theologians, Robert Boylan and Stephen Smoot, to make fun of him and correct him (which Smoot did via Twitter and Boylan did via blog.
But assuming that there may have been an honest seeker who saw Dehlin's tweet and thought the question was meaningful, let's play along. Dehlin seems to think that Nephi and the Prophet Joseph Smith were in the same situation, and they were not. I will allow Nephi to explain his own situation because he does so beautifully:
First, as the opening verses state, Nephi was very hesitant to kill Laban, even though Laban had recently nearly killed his older brother and stolen his father's property. ( 1 Nephi 3:11-26) This shows us that while Nephi had suffered much from Laban, he still respected Laban's humanity and was very hesitant to kill him, showing us that Nephi was not primarily motivated by revenge.7 Nevertheless I went forth, and as I came near unto the house of Laban I beheld a man, and he had fallen to the earth before me, for he was drunken with wine.8 And when I came to him I found that it was Laban.9 And I beheld his sword, and I drew it forth from the sheath thereof; and the hilt thereof was of pure gold, and the workmanship thereof was exceedingly fine, and I saw that the blade thereof was of the most precious steel.10 And it came to pass that I was constrained by the Spirit that I should kill Laban; but I said in my heart: Never at any time have I shed the blood of man. And I shrunk and would that I might not slay him.11 And the Spirit said unto me again: Behold the Lord hath delivered him into thy hands. Yea, and I also knew that he had sought to take away mine own life; yea, and he would not hearken unto the commandments of the Lord; and he also had taken away our property.12 And it came to pass that the Spirit said unto me again: Slay him, for the Lord hath delivered him into thy hands;13 Behold the Lord slayeth the wicked to bring forth his righteous purposes. It is better that one man should perish than that a nation should dwindle and perish in unbelief.14 And now, when I, Nephi, had heard these words, I remembered the words of the Lord which he spake unto me in the wilderness, saying that: Inasmuch as thy seed shall keep my commandments, they shall prosper in the land of promise.15 Yea, and I also thought that they could not keep the commandments of the Lord according to the law of Moses, save they should have the law.16 And I also knew that the law was engraven upon the plates of brass.17 And again, I knew that the Lord had delivered Laban into my hands for this cause—that I might obtain the records according to his commandments.18 Therefore I did obey the voice of the Spirit, and took Laban by the hair of the head, and I smote off his head with his own sword. (1 Nephi 4:7-18)
But to Dehlin's point, notice that Nephi needed the plates of brass in order for future generations to have the law, and furthermore so they would have a visual reminder of their homeland and ancestry. A third reason, though this is not stated, is that the plates would be a means to teaching future generations to read and write, which would not have been possible in the New World. Thus, there were sufficient reasons for Nephi and his family to have the plates of brass.
As for the Prophet, none of these issues applied. The people of his time had both the Hebrew Bible and the New Testament, so they knew the law of Moses and about Christ already. They were a literate people as well, and they needed no reminders of their homelands because many people in Joseph Smith's time were 2nd or 3rd generation Americans who knew where their families had come from. All Joseph Smith needed was to provide people with the text of the Book of Mormon and the Spirit would do the rest (Moroni 10:3-5).
Dehlin also seems to point out that the plates were not used themselves during translation, which is true so far as we know. We do not know entirely how the Book of Mormon was translated, but it seems clear from some third person accounts that the plates were not used in translation. This would be important if Joseph Smith were a linguist and was translating one language into another, but he was not; he was a prophet using divine means to portray a divine message. The word translation is the main problem here because when we see or hear that word we think of the process of the linguist. But, due to poverty of the English language, the word will have to do for now.
John, come on. You are better than this....