All right, there are statements of fact. "Mozart wrote music" is not an opinion.

But "Mozart's wrote wonderful music" is an opinion. "Mozart wrote wonderful music, IMO" doesn't really change things. Actually, it doesn't even mean that, if someone disagrees with this opinion of mine, I am any less likely to hold their opinion on this matter in some contempt.

In fact I do think there is a place for the kind of ritual reminder that much/most of the time we are talking in terms of opinions rather than facts - but I much prefer that to be done through the kind of expressions that have been developed in writing letters, as well as in conversation, rather than through the mechanical use of "IMOs" and so forth.

People keep on implying that communicating through writing is something new, and this seems to me a very strange idea. (Note the IMO equivalent in that sentence.) People have been writing letters to each other for a good few thousand years.