If one wants to "save" them, fine. However I won't waste my time entertaining the superiority of one follower of Christ over another.
It's up to the individual as far as how they handle their relationship with God.
Cb,...the issue isn’t so much one of one religion being superior over another.
Since people want a simple definition of Christianity, keep it simply...faith alone in Christ alone.
Even with this simple definition, the Adversary will twist the basic elements such that one still isn’t in fellowship with God, but distracted by the counterfeit.
For example, many here believe the Christ thought of by the LDS is not the Christ of Scripture, hence a substitute for a real relationship with God.
The best approach to witnessing to such a cult or false believer is to simply communicate and witness the Word of God. No man is going to save a Mormon, rather salvation is only from God, and we might communicate that Word, so that He does all the work in salvation.
I agree with your point that their is volitional responsibility for each believer to handle their relationship with God, which is direct via Christ.