Its not a matter of denotation and connotation. Its much like the word "sin"; thats a specific term for a specific facet of Christian theology, with defined meanings and sets of definitions. There are many different sins, and detailed laws concerning what is a sin and what is not. The name itself is exclusive to Christianity, theologically speaking, and it has specific usages within that theology. But its used in non-Christian contexts. People casually use the word "sin" to describe things that are "bad", things that are immoral or appalling--this is far from the actual Christian definition and usage of the word sin, Biblically speaking, which has specific context. It has evolved a seperate, non-Christian meaning, regardless of the Christian roots that the word has.
This is not quite an exact parallel, but its approximate.

Like I said, the "immaculate conception" is not in the revision I am doing right now, but dogmatic Christians should know that it is used in non-Christian contexts in the manner in which I used it. I appreciate the enthusiasm, but I think you are splitting hairs about something that is, at the very least, debatable, and in most peoples understanding even acceptable.