Fortunately, you can search for "Letter VII" in the Joseph Smith papers and read it directly from Joseph's own history!
You're not offering your views to start an argument, but simply to explain what you believe. If necessary, you can emphasize that the Mesoamerican setting, based on the two-Cumorahs theory, is not Church doctrine and does not reflect Church policy, but we don't want to argue with anyone. We want to educate them, and let them think whatever they want, no problem.
But the ongoing suppression of Letter VII needs to end.
It's quite strange that it's okay for people to give firesides in chapels about Mesoamerica but not about the North American setting. Think about that one.
To be clear, I'm not saying that I think the Mesoamerican theory should also be suppressed.
In fact, I favor more exposure of the Mesoamerican position. I'd like everyone in the Church to compare the North American setting to the Mesoamerican setting. That's why I put a comparison table in my book, Mesomania. And on my consensus blog, here.