As I read the threads responding to questions regarding Mormons and their beliefs, I detect an almost paranoid temperament, one that suggests irrationality regarding what they teach.
Our Lord Jesus Christ faced the same challenge, whatever he did or taught was challenged by the authoritative religious elite; “And all the people were amazed, and said, Is not this the son of David? But when the Pharisees heard [it], they said, this [fellow] doth not cast out devils, but by Beelzebub the prince of the devils.” (Matt 12: 23,24)
It is true to say that the greatest risk to any establishment is always from within and Holy Scripture teaches us that Jesus Christ warned that it was “He that dippeth [his] hand with me in the dish, the same shall betray me.” (Matt 26: 23) It was Judas, a disillusioned and reprehensible disciple, who ultimately set in train what some perceived would be the end of the vexatious teacher from Galilee and his cult.
But it was not the end because what ever seeks to destroy the work of God ultimately and unwittingly contributes to its fulfilment but will never share in the eschatological glory promised to the truly faithful.
The threat to Roman Catholicism has always come from within;
Mormonism or to be more precise The Church of Jesus Christ of Latter-day Saints, did not begin from the efforts of a disillusioned Catholic and to quote the words of Gamaliel (Acts 5:38,39)
“So in the present case, I say to you, stay away from these men and let them alone, for if this plan or action is of men, it will be overthrown; but if it is of God, you will not be able to overthrow them; or else you may even be found fighting against God.”