I'd say that it sure is. I can't help but recall
G. K. Chesterton's famous essay on Mormonism, and in particular this part of it:
Our real error in such a case is that we do not know or care about the creed itself, from which a peoples customs, good or bad, will necessarily flow. We talk much about respecting this or that persons religion; but the way to respect a religion is to treat it as a religion: to ask what are its tenets and what are their consequences. But modern tolerance is deafer than intolerance. The old religious authorities, at least, defined a heresy before they condemned it, and read a book before they burned it. But we are always saying to a Mormon or a MoslemNever mind about your religion, come to my arms. To which he naturally repliesBut I do mind about my religion, and I advise you to mind your eye.
...
Historians seem to have completely forgotten the two facts first, that men act from ideas; and second, that it might, therefore, be as well to discover which ideas.
Since I am a Christian I must believe that a person's religion is important. People of different religions acts differently because they believe different things. Before I vote to put of Mormon in the White House, it's worth asking what he actually believes in. If I find that Mormon doctrine historically insists that they 'Prophet' and 'Apostles' are supreme because of being in direct contact with God, that they perceive themselves as having the authority to override the basic teachings of the gospels, and so forth, that has bearing on whether I'd want one governing my country. To me this is bleedingly obvious.
Consider a few facts about Mormon history. Consider, for instance, the fact that until 1978 the Mormons taught that black skin was god's curse for moral inferiority. If Romney was a believing Mormon then he believed this for half his life. Consider that the leadership of the LDS church is constantly rewriting its own history to cover up embarrassments and that a lot of what they say is flatly untrue. Do we want a person who plays along with that sort of thing to lead our country?