"There are a series of brief skits, designed to offend, about how the Book of Mormon came to be, and while these struck me as unnecessary"
The idea that the skits they were created deliberately " to offend" is simply incorrect. The two skits (at the start of each Act) were used to give the audience a basic idea on the fundamentals of the Book of Mormon (the scripture). Most people haven't ever heard of the Nephites or the Lamanites, and they certainly don't know where they came from, what happened to them, or even how Joseph Smith came to find the plates which contained the records of these ancient people. The point of the skit is to give the audience a quick and, yes, humorous overview of the complex subject. Otherwise, there would be plenty of parts of the musical that people would not get. If you were actually offended, then I'm thinking it just flew over your head.