Many popular qualifiers don’t have clear meaning. As lsusr noted, there is a sense in which the qualifier in “I think Z” is usually either empty of content or a lie. At the same time, applying charity to the uses of the more general “It’s my opinion that Z,” it’s easy to see at least four good uses: (1) communicating a hypothetical without claiming any credence, (2) expressing a belief without offering a justification, (3) communicating uncertainty, (4) expressing uncertainty without offering a justification. But for those uses “opinion” is not a good qualifier. For hypotheticals, it’s better to say “Consider the possibility that Z.” For beliefs, it’s “I believe Z, though I’m not going to discuss my reasons right now.” For uncertainty, it’s better to quantify the uncertainty, saying “It’s not unlikely that Z, because J.” And nobody tries to say things like “I believe it’s not unlikely that Z, though I’m not going to discuss my reasons right now.” (So perhaps just saying “opinion” is a sensible shorthand for all the possibilities, as long as the abominable ambiguity of the qualifier is understood.)
In the last case, not discussing reasons for choice of credence is similar to not discussing reasons for a belief. What you should put out into the world then is a claim about your own state of mind, as making sensible use of it requires distinguishing it from the underlying claim about the world. It’s only when you do offer justification (or expect it to be apparent) does it make sense to insist on the underlying claim itself. Even then, it’s better (more modular!) to communicate arguments, not conclusions (likelihood ratios, not credences).
Many popular qualifiers don’t have clear meaning. As lsusr noted, there is a sense in which the qualifier in “I think Z” is usually either empty of content or a lie. At the same time, applying charity to the uses of the more general “It’s my opinion that Z,” it’s easy to see at least four good uses: (1) communicating a hypothetical without claiming any credence, (2) expressing a belief without offering a justification, (3) communicating uncertainty, (4) expressing uncertainty without offering a justification. But for those uses “opinion” is not a good qualifier. For hypotheticals, it’s better to say “Consider the possibility that Z.” For beliefs, it’s “I believe Z, though I’m not going to discuss my reasons right now.” For uncertainty, it’s better to quantify the uncertainty, saying “It’s not unlikely that Z, because J.” And nobody tries to say things like “I believe it’s not unlikely that Z, though I’m not going to discuss my reasons right now.” (So perhaps just saying “opinion” is a sensible shorthand for all the possibilities, as long as the abominable ambiguity of the qualifier is understood.)
In the last case, not discussing reasons for choice of credence is similar to not discussing reasons for a belief. What you should put out into the world then is a claim about your own state of mind, as making sensible use of it requires distinguishing it from the underlying claim about the world. It’s only when you do offer justification (or expect it to be apparent) does it make sense to insist on the underlying claim itself. Even then, it’s better (more modular!) to communicate arguments, not conclusions (likelihood ratios, not credences).