A little history and some corrections
I don't have time today to retype it all or even go looking for it, but a search of the archives here and/or at utahconcealedcarry.org should turn up a couple of posts from me about the history of this particular law.
To be brief, churches have long had the legal ability to ban guns from their property in Utah, they just had to post signage to that effect. Some 10 or 12 years ago, shortly after we strengthened State preemption to make clear that public school teachers and most other government employees were protected against anti-RKBA discrimination in the workplace (ie allow them to carry on the job), a citizens' petition was started to ban all private guns--including those carried by persons with permits--from both schools and churches: "Safe to Learn, Safe to Worship" they called it. The LDS Church considered joining the petition so as to keep guns out of their churches without having to post signs. I was involved in a meeting with the LDS legal counsel and lobbyist, along with other leading pro-RKBA organizations and a solid pro-RKBA legislator to see if we could work out a deal to keep the LDS Church from throwing its considerable political weight behind that effort.
We arrived at the current law that allows churches to give notice in several different ways, including the BCI public web page. Last I checked, the LDS and one other church were using that method, while a couple of downtown SLC churches had signage posted. True to their word, the LDS Church did not get involved in the petition drive and it failed to make it onto the ballot.
When we pushed for "Parking Lot Preemption" we specifically exempted religious employers so as to keep the LDS (and Catholic and other) church(es) from having any legitimate dog in the fight. Once they saw they were exempted, they stayed out of that one and we managed to win that battle against the gun grabbers and business interests.
I have never understood why the LDS church wants to ban private guns in their Houses of Worship. I could speculate, but I doubt it would add anything of value to the discussion, and of course, we all here would certainly disagree with whatever reasons (short of direct revelation) might be given anyway. Neither the legal counsel nor the lobbyist could or would ever give any reason beyond church leadership wanting it. They did want a stiffer penalty than infraction to encourage compliance. We pushed back against that and argued that gun owners and permit holders were not only law abiding, but also polite and respectful and those who knew the policy would abide it regardless of the level of legal penalty, and we didn't want a rare, unintentional violation to cause someone to lose his permit or worse. We won that discussion and the penalty for violation has remained at the infraction level.
The policy is contained in the Handbook of Instruction, Book 2, on page 192, available at <https://www.lds.org/bc/content/shared/content/english/pdf/language-materials/08702_eng.pdf?lang=eng>.
"Firearms
Churches are dedicated for the worship of
God and as havens from the cares and concerns
of the world. The carrying of lethal weapons,
concealed or otherwise, within their walls is
inappropriate except as required by officers of
the law."
My personal view on the matter is this:
This is not the policy I would set were it my right or obligation to set such policies. But it isn't. And as an active LDS, three or four times a year I sustain Thomas Monson as not only the Lord's Prophet on the earth, but also as President of the LDS Church. In other words, it is his right and duty not only to receive revelation and declare the official doctrines of the church, but also to set mundane temporal policies so long as those policies do not conflict with doctrine or eternal salvation. As President Woodruf taught in the excerpts from talks on the Manifesto (Notes on Official Declaration 2 in the Doctrine & Covenants), the Lord will not allow His Prophet to lead His people astray.
So for active LDS, there is really not much room for questioning here. Whether the policy was based on some revelation from the Lord, or is simply a mundane administrative policy, it is not contrary to the Lord's will. Nor will adherence to it negatively affect eternal salvation. I believe active LDS have an obligation to follow the policy in the absence of direct, personal revelation to the contrary. Not merely some different understanding of various scriptures and doctrines, but an actual, direct revelation. I firmly believe and hope that by sustaining the prophet by following a policy I don't care for, I will be in a position to be warned what day not to be in church, rather than needing to use deadly force. That is my view.
Non-LDS are not obliged to believe anything about Thomas Monson or LDS beliefs. But a decent respect for what others hold sacred should give them serious pause before violating both stated requests and statutory law regarding guns in LDS houses of worship. I believe the policy should be followed, one way or another. One easy way to follow the policy is to simply not enter an LDS house of worship. That is pretty sure to keep your gun outside. If one is going to enter an LDS house of worship, I believe one should obey the policy by leaving the gun out.
That all said, if one is going to make a deeply personal decision to violate a gun law--any gun law, no matter how mundane--it should go without saying that one should not broadcast that intent (even in veiled hypotheticals) on an open, publicly readable board. Not only could it harm your legal case if ever charged, but it harms the image of the entire community of gun owners. If a man has received personal revelation to carry despite the policy, such things are deeply personal and should be kept personal: pearls and swine kind of thing.
I would not expect petitions or letters to make any change in the policy. And unlike some other issues, the media certainly is not friendly to RKBA in churches or darn near anywhere else.
If someone is a personal friend or close relative to a general authority, that might be a place to start a discussion and I'd love to be involved if anyone wanted me to be.
Charles