Exactly right.
Jesus said that we should not judge what any person’s final fate will be. But He also said, according to Paul, that when a fellow Christian starts spreading obvious errors, the first thing you shoul do is quietly correct him. And then publicly correct him or even throw him out of the Church if he refuses to amend his errors.
To say that Mormons are Christians like everyone else simply is not true. It contradicts several Mormon teachings, including most importantly the teaching that Jesus is only another human being. No divinity for Jesus, no Trinity for God.
That is not to say that Mormons do not have a right to believe what they like, but rather to say that it is NOT Christian according to the normal sense of the word.