What has the LDS Church (Mormons) historically taught about the Curse of Cain and dark skin? I have heard that people with black skin had been denied certain things in the Mormon Church until the past 30 years or so and that this has something to do with the Curse of Cain.  What has been the historical teaching of the LDS Church regarding the Curse of Cain and dark-skinned people?  What are the references in the Book of Mormon and other Mormon Scriptures that address this issue?
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.

http://en.wikisource.org/wiki/Book_of_Mormon/2_Nephi#5:21


  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:

http://en.wikisource.org/wiki/Book_of_Mormon/3_Nephi#2:15


  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:

http://en.wikisource.org/wiki/Book_of_Mormon/Alma#3:18


  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.

http://en.wikisource.org/wiki/Book_of_Mormon/2_Nephi#26:33


  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
  Gentile.


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.

http://en.wikisource.org/wiki/Book_of_Mormon/Jacob#3:8


  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.