I believe the reason is because of a couple of things:
a. This is a Studies of Latter-Day Saints Board and does not cover other off shoot religious groups. Your question with the mention of Warren Jeffs should probably have gone here:
Source 2b. The other reason is to understand the concept Doctrinally will also require the person asking to have a foundation in the background of the early Church of Jesus Christ of Latter-Day Saints and the revelations received on the subject. That is NOT covered here, it is not even covered in the public LDS Doctrine Board just because as you say "This is getting more confusing...". That is why in this Community certain Topics are covered only in what we call an LDS Mature section.
Now with that said I would like to try and clear up with simple statements any misunderstanding over this Topic:
1. The term "Mormon" is a celebrated nickname because of our use of the Book of Mormon. Essentially anyone believing the Book of Mormon to be the word of God may refer to themselves as "Mormon", but not necessarily be part of the
main body of the Church known as "The Church of Jesus Christ of Latter-Day Saints".
The early Church of Jesus Christ of Latter-Day Saints did practice polygamy as authorized by the then Church leaders.
2. During a certain period the Church was harassed by the US government about the practice and a manifesto was issued abolishing the practice.
3. Off shoot groups formed their own leadership to continue the practice using the term "Mormon" as explained in point #1.
4. The main Church of Jesus Christ of Latter-Day Saints reaffirms that it does not practice polygamy to date.
I hope this makes it clear and understandable.
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