Which sounds more appropriate?:

1.  My opinion is that vanilla ice-cream is the best flavor of ice-cream.
2.  My conviction is that vanilla ice-cream is the best flavor of ice-cream.

I think most people would go with option 1, but why?  The denotative meaning of “opinion” and “conviction” allows for both usages, but the connotative meaning is quite different.  “Opinion” connotes a weak epistemic viewpoint.  When someone says they have an opinion on a matter, we tend to think there was little, if any research that went into forming their viewpoint.  “Opinion” has subjectivity and personal taste written all over it.  “Conviction,” on the other hand, connotes a much stronger epistemic viewpoint.  When we hear someone say their conviction is that X is true, we tend to think there was at least a fair amount of research that was instrumental in forming their conclusion.  A conviction is not entirely subjective, but based in some facts.

I would not make a doctrine out of this, but it seems to me that when we are speaking of our perspective on matters of objective truth, that we couch them in terms of our “conviction” rather than in terms of our “opinion.”  Opinion seems better reserved for matters of subjective truth like one’s favorite flavor of ice-cream.  Conviction bespeaks rational persuasion.  This is important in a culture in which religious claims are presumed to be flavors of ice-cream, with everyone simply picking the flavor that appeals to their tastes.  We need to make it clear that we do not have mere opinions on religious matters, but have developed genuine convictions through researching matters of objective fact.