First, I think it is not surprising that the Mormon issue has not been perceived as a big issue. Most of the folks who believe this is a valid issue aren't about to go out and say so publicly.
For some voters, it may be latent biases. For others, they are aware that publicly opposing Romney -- because of his religion -- would be viewed as politically incorrect.
Either way, it wouldn't surprise me one bit if Romney's campaign was seeing internal numbers that differed from what everyone was "saying" about whether or not they would vote for a Mormon.
Patrick also wrote: "Perhaps the Romney campaign knows something we don't? That Mormonism is a bigger deal on the ground than we are given to believe from press reports?" I think he's right.
Bottom line: What people say in polite company -- and what they actually do -- are two different things. Clearly, Mitt Romney's team believes this is something they must do.
Aside from the empirical evidence, though, there may be another reason the speech is going to happen. I hate to use this analogy, because I don't want it to appear that I believe Mitt Romney is guilty of anything, but I would equate Romney's desire to give a speech to a defendant's desire to take the stand in his own trial. While an attorney may advise his client not to take the stand, a man who believes he is innocent wants to have his say, and then accept his fate.
My gut instinct is that Mitt Romney will be able to accept losing only if he feels he was able to make his case to the voters. Losing, without making ones case, would be the worst feeling in the world.
In a related story, over at RedState, Erick posits the theory that the so-called push-polling that occurred over Thanksgiving week was actually Romney's team testing to see how badly this issue hurt him.
Based on the fact that the speech will come a few weeks after the calls went out, that theory is not an absurd one to make ...