Have you forgotten the 1st amendment? It guarantees a freedom of expression that is found in few other nations. It doesn't mean you need to listen, or even respect other opinions, but the right exists to express it.
Back to christian-mormon differences.
As a lds, you understand only that your church teaches from the Bible, BoM, PoGP, etc, and that Jesus was in fact not only a historical figure, but the physical Son of the Father - right?
This is where mormonism parts company with mainstream christianity: Christianity teaches the trinity is the one and the same, not three distinct individuals. The lds concept is easier to comprehend IMO.
The Book of Mormon vs the Bible: Christianity takes a dim view of any other writing that also claims to be scriptural canon - period. The BoM's attempt to placate that by stating it is "another testament" of Jesus Christ does not make it acceptable to christianity just because it said so. The Bible has been studied and dissected and libraries dedicated to it's composition, history and authorship for thousands of years, from both theological and scientific viewpoints.
The book of Mormon by contrast, has only been available since 1830, but has been also scrutinized by the same processes. The difference being that the BoM fails to live up to it's claims as history and authenticity.
That generally does not bother the mormon membership at large, as they simply blame that as a deception of satan. This concept invalidates and frustrates any further discussion, and in fact, discussion regarding the BoM "historicity" is discouraged with in the church.
I won't go into the Book of Abraham, but the same reasoning applies.
The schism between the two sects are stark and revealing. Adherents to either side can be forgiving, like you, or obnoxious and defiant. Others simply parrot back scriptural quotes they may or may not understand completely.
Bottom line is human nature and the anonymity of the internet. Religion is a big button that says "Don't Push Me!", and the usual response is a big finger pushing down.