Walther said:
As far as the LDS Church is concerened, the Brethern have said not to carry in the church so I don't, but that is just me and I don't judge others in what they do.
Those following the first principal of concealed carry, "Concealed" (that includes keeping your, and your families mouths shut), are highly unlikely to be discovered at any non-secured location.
The following is purely hypothetical:
Do you really think any church would excommunicate or prosecute members who stood up in an emergency willing to give his or her own life for the protection of others, just because they used a prohibited tool to stop harm from becoming the innocent? I suspect that the church officials might even work to persuade the government from pursuing charges.
Purely speculation on my part. Please always obey the law.