When Mormonism excommunicates or disfellowships people who aren’t faithful to Mormonism or believing in Mormonism, it helps both Mormons and evangelicals. It adds clarity to identity and worldview. It contributes to religious integrity. It speeds up the process of people re-evaluating their beliefs.
We’re better off interacting with Mormons as Mormons, agnostics as agnostics, and atheists as atheists. When the waters are muddied, and I have to parse between committed Mormons, cultural Mormons, New Order Mormons, Jack Mormons, agnostic Mormons, atheist Mormons, etc., it takes away from time and focus spent on actually promoting the truth.
For this reason, I would be glad if every religion excommunicated or disfellowshipped all of its unfaithful or unbelieving members. Evangelicals are better off too if we do this. It also happens to be biblical (1 Corinthians 5).