We're certainly thinking alike. My response to the lecture was to take my LDS friend to Galatians 1. The conversation ended shortly after that but by the look on his face, it was clear that Paul's cursing of those who brought a different gospel from an "angel of heaven" rattled him. Galatians 1:8 strikes right at the heart of the foundations of Mormonism by cursing the exact situation that gave rise to the "First Vision."
That conversation took place about 15 years ago and I've long since lost connection with this Mormon but I have always thought that the Holy Spirit planted a seed there that would bear fruit later.
They can't defend their theology because it is inconsistant with Christian thought and is no theology whatsover.
In fact, I have an idea that there are no accepted Mormon theologians given recognizence anywhere in Christian theological realms unless you know of some? I would be happy to read them if there are any.
One other verse that proves that Christ's church was never lost and "re-found" is Psalm 102:12
But thou, O LORD, shalt endure for ever; and thy remembrance unto all generations