1. BMC scholars are unaware of important sources Joseph drew upon; and
2. Some Christians are so focused on rejecting the Book of Mormon that they ignore Christian ideas the pre-dated the Book of Mormon.
The Kno-Why addresses the passages in the Book of Mormon and D&C that describe Christ bleeding from every pore:
Mosiah 3:7 And lo, he shall suffer temptations, and pain of body, hunger, thirst, and fatigue, even more than man can suffer, except it be unto death; for behold, blood cometh from every pore, so great shall be his anguish for the wickedness and the abominations of his people.
Doctrine and Covenants 19:18 Which suffering caused myself, even God, the greatest of all, to tremble because of pain, and to bleed at every pore, and to suffer both body and spirit—and would that I might not drink the bitter cup, and shrink—
The New Testament says nothing about pores. It says only this:
And there appeared an angel unto him from heaven, strengthening him. And being in an agony he prayed more earnestly: and his sweat was as it were great drops of blood falling down to the ground” (Luke 22:43–44).
Other translations render this passage to say "his sweat became like great clots of blood" and similar variations, as discussed here.
Talmage discusses the issue in Jesus the Christ, which you can see here:
Like BMC, Christian scholars have debated over the meaning and even origins of Luke 22:43-4. Such debates can never be resolved, which is why the intellectuals love them. Full employment, etc.
Here's how BMC explains it:
In other words, based solely on the manuscript evidence and the understandings of ancient Christian writers, while the matter of whether these verses are original to Luke’s gospel cannot be fully resolved at the present time, there are, however, enough reasons for one to cautiously accept their factual authenticity while still being aware of their questionable textual status.
This is stereotypical M2C rhetoric. Next, they claim superiority over their Christian peers:
The issues surrounding the authenticity of Luke 22:43–44 and whether Jesus sweat actual blood or merely sweat as though he were bleeding will likely remain open to debate among biblical scholars for many years to come. Latter-day Saints, however, have additional scriptures that tip the scales in favor of these verses being authentic and also describing a real physiological phenomenon.
This is not an irrational point, but here's a key to understanding the passages that BMC ignores.
As near as I can determine, the first Christian writer to claim that Christ sweat actual blood from every pore was James Hervey, published in 1764 and subsequent editions.
Here, Hervey has Christ suffering and bleeding in Gethsemane (the prelude to his last suffering).
Why is Hervey important? Because his books were on sale in Palmyra in 1819, and Joseph donated a Hervey book to the Nauvoo Library in 1844. Hervey was a significant influence on Joseph's vocabulary, as I'm showing in an upcoming book.
Notice too that Hervey wrote about Christ's pangs as exquisite. Compare that to D&C 19:15.
Doctrine and Covenants 19:15 Therefore I command you to repent—repent, lest I smite you by the rod of my mouth, and by my wrath, and by my anger, and your sufferings be sore—how sore you know not, how exquisite you know not, yea, how hard to bear you know not.
Anti-Mormon Christians criticize these passages, claiming that the atonement did not occur in Gethsamane.
This is the type of argument that comes across as argumentative purely for the sake of argument, but when they make such arguments, they are ignoring their own tradition, such as James Hervey's work.