Here is more context for some verses from the Book of Mormon, the first quote shows the curse, and the effect of it, so they became dark-skinned and lazy. The problem is that this can then be extended to shape prejudices against anyone because of their skin color, but, the last two quotes shows that discrimination based on color is wrong, and all from the Book of Mormon.
21 And he had caused the cursing to come upon them, yea, even a sore cursing, because of
their iniquity. For behold, they had hardened their hearts against him, that they had become
like unto a flint; wherefore, as they were white, and exceedingly fair and delightsome, that
they might not be enticing unto my people the Lord God did cause a skin of blackness to come
upon them. 22 And thus saith the Lord God: I will cause that they shall be loathsome unto
thy people, save they shall repent of their iniquities. 23 And cursed shall be the seed of
him that mixeth with their seed; for they shall be cursed even with the same cursing. And
the Lord spake it, and it was done. 24 And because of their cursing which was upon them they
did become an idle people, full of mischief and subtlety, and did seek in the wilderness for
beasts of prey.
When you come back to God and do what is expected then this curse is lifted:
12 Therefore, all the Lamanites who had become converted unto the Lord
did unite with their brethren, the Nephites, and were compelled, for
the safety of their lives and their women and their children, to take
up arms against those Gadianton robbers, yea, and also to maintain
their rights, and the privileges of their church and of their worship,
and their freedom and their liberty. 13 And it came to pass that
before this thirteenth year had passed away the Nephites were
threatened with utter destruction because of this war, which had
become exceedingly sore. 14 And it came to pass that those Lamanites
who had united with the Nephites were numbered among the Nephites; 15
And their curse was taken from them, and their skin became white like
unto the Nephites; 16 And their young men and their daughters became
exceedingly fair, and they were numbered among the Nephites, and were
called Nephites. And thus ended the thirteenth year.
Another section showing that others may get the curse due to their wickedness:
14 Thus the word of God is fulfilled, for these are the words which he
said to Nephi: Behold, the Lamanites have I cursed, and I will set a
mark on them that they and their seed may be separated from thee and
thy seed, from this time henceforth and forever, except they repent of
their wickedness and turn to me that I may have mercy upon them. 15
And again: I will set a mark upon him that mingleth his seed with thy
brethren, that they may be cursed also. 16 And again: I will set a
mark upon him that fighteth against thee and thy seed. 17 And again, I
say he that departeth from thee shall no more be called thy seed; and
I will bless thee, and whomsoever shall be called thy seed, henceforth
and forever; and these were the promises of the Lord unto Nephi and to
his seed. 18 Now the Amlicites knew not that they were fulfilling the
words of God when they began to mark themselves in their foreheads;
nevertheless they had come out in open rebellion against God;
therefore it was expedient that the curse should fall upon them. 19
Now I would that ye should see that they brought upon themselves the
curse; and even so doth every man that is cursed bring upon himself
his own condemnation.
When you try to be consistent with the BoM then cherry-picking to justify prejudices is going to happen, as God isn't going to discriminate based on skin color for example.
33 For none of these iniquities come of the Lord; for he doeth that
which is good among the children of men; and he doeth nothing save it
be plain unto the children of men; and he inviteth them all to come
unto him and partake of his goodness; and he denieth none that come
unto him, black and white, bond and free, male and female; and he
remembereth the heathen; and all are alike unto God, both Jew and
And here the believers are commanded not to hold these against others since the believers should reflect on the filthiness of their own souls. This is similar to "Him who has no sin cast the first stone", IMO.
7 Behold, their husbands love their wives, and their wives love their
husbands; and their husbands and their wives love their children; and
their unbelief and their hatred towards you is because of the iniquity
of their fathers; wherefore, how much better are you than they, in the
sight of your great Creator? 8 O my brethren, I fear that unless ye
shall repent of your sins that their skins will be whiter than yours,
when ye shall be brought with them before the throne of God. 9
Wherefore, a commandment I give unto you, which is the word of God,
that ye revile no more against them because of the darkness of their
skins; neither shall ye revile against them because of their
filthiness; but ye shall remember your own filthiness, and remember
that their filthiness came because of their fathers.
So, it is easy to see how people could pick some verses and make some decisions that enforce their own biases, but that is due to ignoring other verses, so the blame is not on the BoM but on those that did the cherry-picking.