Encyclopedia of Mormonism, pg. 953; “Because of the angel Moroni’s role in restoring the everlasting gospel to be preached to all the world (cf. Rev. 14:6-7; D&C 133:31-39), the Church placed a statue depicting him as a herald of the Restoration atop the Salt Lake Temple, and later on the hill Cumorah near Palmyra, New York, where anciently he had buried the Book of Mormon plates. Copies of the statue have also been placed atop several other LDS temples.”
Isaiah 45:16; “They shall be ashamed, and also confounded, all of them: they shall go to confusion together that are makers of idols.”
Placing a statue of a dead man on top of your place of worship is called idol worship. Especially since you’re going into that temple to do works for the dead. It’s a form of necromancy.