Burn,
I agree that it's best to conclude amicably. But I'm more conservative than you about God's view of "a sincere heart that labors in error." Saul of Tarsus engaged in such labor until he saw the light. When his error was shown to him, he made an about-face in his beliefs and life-goal. It's good he did since God doesn't look kindly upon obstinacy and stubbornness. What God expected of Saul, he and Christ expect of us.
Even while the apostles were alive, some Christians were trusting in "another Christ" to save them. Rather than dismiss that as simply "a poor reflection" of the truth or as "imperfect knowledge to a greater or lesser degree," the apostle Paul gave this chiding and warning: "I am afraid that, as the serpent deceived Eve by his craftiness, your minds will be led astray from the simplicity and purity of devotion to Christ. For if one comes and preaches another Jesus whom we have not preached, or you receive a different spirit which you have not received, or a different gospel which you have not accepted, you bear this beautifully." (2 Corinthians 11:3, 4)
Even more forcefully, he scolded: "I am amazed that you are so quickly deserting Him who called you by the grace of Christ, for a different gospel; which is really not another; only there are some who are disturbing you and want to distort the gospel of Christ. But even if we, or an angel from heaven, should preach to you a gospel contrary to what we have preached to you, he is to be accursed! As we have said before, so I say again now, if any man is preaching to you a gospel contrary to what you received, he is to be accursed! (Galatians 1:6-9) [Underlining mine.]
I haven't presented "another Christ." I've advocated what the Bible teaches about Christ, not what tradition or orthodoxy teaches. Contrary to the simple truth of the Bible, an entire system of "salvation" has evolved over the past 2,000 years that totally obscures the simple truth of the gospel as Jesus taught it.
I urge you to look at the picture very carefully. I hope you will take seriously the warnings against "another Christ." I'm sure that heaven will bestow a wondrous outcome.
God bless,
fjtoth