This is a very important point. Heresies like Mormonism are not dangerous or bad just because they're theologically wrong in some sort of detached, academic/intellectual sense -- they have actual deleterious effects on the peoples' conception of God and their ability to have faith in God. They really do damage people's faith, often fatally.
ALL of those who keep the commandments of LOVE WILL be saved. Christ promised it and His word is truth. He also taught us how that He and the Father are one in glory and perfection:
(New Testament | Luke 10:25 - 28)
25 ¶ And, behold, a certain lawyer stood up, and tempted him, saying, Master,
what shall I do to inherit eternal life?
26 He said unto him, What is written in the law? how readest thou?
27 And he answering said, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy strength, and with all thy mind; and thy neighbour as thyself.
28 And he said unto him, Thou hast answered right:
this do, and thou shalt live.
(New Testament | John 17:21 - 23)
21 That they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me.
22 And
the glory which thou gavest me I have given them; that they may be one, even as we are one:
23 I in them, and thou in me, that
they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me.