[zzo38computer]

As I understand, LDS did not add another book to the Bible; Book of Mormon is not a part of the Bible, although (as far as I know) still considered a scripture according to LDS.

(Nevertheless it is the reason I had thought of too (many years ago), although other people have cited different reasons.)

[siliconpotato]

Joseph smith claims to have had a new revelation and the book of Mormon is "another gospel". It's fan fiction for Americans and claims that the church became corrupted and are restoring the true church with their non biblical ideas. As such, their ideas are sufficiently divergent from biblical doctrine they are considered not part of the Christian church.

[Slothrop99]

Well, the New Testament (what Christians care about) is entirely set in the historical first century Roman Empire [0], all places are accurate and known to exist.

The Book of Mormon postulates some fantasy world perhaps not unlike Middle Earth? And also weird theological stuff from 19th century science-fiction? Sorry, that is a different religion.

[0] expect for the last book of revelations of the future.

[Daviey]

Why do you feel it is outsiders role to tell them they are not Christians, surely it's their role to self-determine?

[Slothrop99]

Why do you feel that most christian sects cannot decide they are heretics? We're not talking about some Lutheran Synod politics BS, they have this whole fantasy/scifi book and theology.

Obviously it's a free country, so they can say whatever they want.