“Keith Ellison isn’t POTUS. There’s a whole world of difference”
There is, but a difference of degree, not kind. Romney swearing in on the book of Mormon wouldn’t make the book of Mormon as legitimate as the Bible for those paying attention any more than Ellison’s swearing in did for the Koran for those who were watching. What they swear on depends on what is important to them.
It being involved in a ceremony with such publicity would increase the number of rubes who take it to mean more than it means, yes. But they would be rubes, and no one need listen to them. If it still bothers you, don’t elect a Mormon.
“I’m quite sure the US populace would frown on it.”
Yeah, but so what? It shouldn’t, firstly. More importantly if it doesn’t bother them enough not to elect a Mormon, they get what they deserve.
That is something that I will NOT do.