Someone is wrong, either all the Christian denominations scholars, or else the cult that a Missouri guy created in the 1800s. Christianity seems unified in the analysis that the Joe Smith religion is a different religion than Christianity.
“The Decree on Ecumenism (Unitatis Redintegratio) of Vatican II teaches that “all who have been justified by faith in baptism are members of Christ’s body, and have a right to be called Christian, and so are correctly accepted as brothers by the children of the Catholic Church.”
Because Mormonism is polytheistic and rejects the Trinity, Mormon baptism is not valid, and Mormons are not considered separated brethren. For the same reason, outreach to them, while certainly a good thing, is not ecumenism, though it can include dialogue and social cooperation as well as efforts to evangelize them.”