First, let me explain that term. As anyone who has read the Mesomania book knows, I think Mesomania is not really a choice; it's a psychological condition that is nearly universal among LDS because of the artwork and educational materials--including Church manuals and magazines--that we've all been exposed to since childhood. Mesomania is one of the first elements of Mormonism that investigators learn about because of the artwork in the blue editions of the Book of Mormon. So it's no one's fault that they have Mesomania; it's something every LDS has to some degree.
Consequently, I don't think the term Mesomaniac applies to the vast majority of the members of the Church. I reserve that term for people who are so obsessed with the Mesoamerican setting that they can't tolerate alternative ideas.
In the last few days, I've had a shocking number of people tell me stories of how they've been treated by Mesomaniacs. These Mesomaniacs include CES faculty, Priesthood leaders, and fellow ward members. In many cases, challenges to the Mesoamerican theory is met with charges of apostasy, shunning, and even attempts to shame. It's deplorable, to use a suddenly popular expression.
I attribute this Mesomaniacal reaction to defensiveness, actually. The basic premises of the Mesoamerican theory are so indefensible, in my opinion, that when challenged, proponents have no alternative but to lash out this way.
I need to clarify another point. There are some proposed Mesoamerican settings that also accept the New York Cumorah. By my definition, those are not a result of Mesomania. In fact, Arnold Friberg himself depicted the New York Cumorah, not some mountain in Mexico, and if we had left that painting in the blue editions, we'd have fewer problems than we have now.
The real problem with Mesomania is when it leads to the rejection of Oliver Cowdery, Joseph Smith, and David Whitmer when it comes to the Hill Cumorah in New York. IOW, Mesomania = the Two-Cumorahs approach. In many cases, it is driven by the conviction that Joseph Smith wrote the anonymous articles in the 1842 Times and Seasons. Some of the Mesomania scholars have told me those articles are not a significant factor in their deliberations and I accept that. There is zero historical evidence that Joseph wrote those articles. But among many, many members of the Church, Joseph's authorship of these anonymous articles is fundamental and turns them into Mesomaniacs.
For now, let me suggest this. If you're in a CES class (broadly defined to include seminary, institute, Sunday School, BYU (any campus), a fireside, etc.) and someone promotes the Mesoamerican theory, you're perfectly entitled to observe that the Church has no official position on Book of Mormon geography. If, as happens far too often, the presenter argues that all the scholars agree, you should 1) point out that not all the scholars agree, 2) that there is no doctrinal reason to accept or even rely on what any scholar says, and 3) ask if he/she has read Letter VII. You'll soon see that the presenter has never heard of Letter VII. Or, if they have, they haven't read it. Instead, they've read some dismissive obfuscation in FairMormon, the Interpreter, or the like.
All we want is for people to read and consider Letter VII. Everyone in the Church during Joseph's lifetime was familiar with it and accepted it. There are some LDS scholars today who insist Oliver Cowdery made it up, or was speculating, and therefore they insist that either way he was wrong. They're entitled to their opinions and the consequences that flow from undermining the credibility and reliability of one of the Three Witnesses (who was the Assistant President of the Church when he wrote Letter VII), but you're not obligated to agree with them.
No one is.
We want every member of the Church to become educated on this specific issue and then to reach his/her own conclusions.
So if you haven't read Letter VII, yet, do it right now. If you have, share it with everyone you know.
And if people call you an apostate for talking about Letter VII, remind them you're reading it out of Joseph's personal history and have them search it for themselves in the Joseph Smith Papers.
NOTE: Letter VII is far from the only problem with the Mesoamerican theory, but it is a fundamental document in Church history that every member of the Church today should be familiar with. Portions of Letter I are already included in the Pearl of Great Price, and in my opinion, portions of Letter VII should be added. It is that fundamental to understanding the Book of Mormon, not only its geography but the covenant and promises it contains. I doubt that will happen anytime soon, but now that the Joseph Smith Papers are available to anyone with Internet access, anyone can read Letter VII in Joseph's own history.