It seems that many people who I would call "intellectually honest" end up developing speech patterns to avoid (1) speaking in absolutes; and (2) making statements of opinion articulated as statements of fact. An example of (1) is to use the words "many" or "most" instead of "all". An example of (2) is to start opinions with "I think".

Those speech patterns, though, can lead to writing which is bland and less than forceful, full of justifications with no interesting assertions to be found. One huge plus of this belief metadata, as you note, is that it frees the author to make bold and daring statements (and hopefully back them up) without committing to the truth of those statements. I think it can make for great writing – the style of strong and passionate assertion mixed with (via the disclaimer) the sensibilities of a reasoned opinion.