I was quoting a previous poster's preference for the use of the masks as in Asia for anything from a "slight cold" so I have no idea what he meant - and this was not even in the context of on a LOB. Folks in many Asian countries seem wear them everywhere - even outdoors which, in my opinion is silly (like the folks I see driving around in their car with a mask on when no on else is in the car - lol) unless wearing for air pollution reasons .How "slight" and how do you know it's going to improve rather than worsen? "Slight" like the kind of symptoms that might prevent any of us from being able to dive? There's nothing "slight" about me being unable to dive on a liveaboard I paid thousands of dollars for because a sick fellow passenger takes no measures to help prevent infecting others. If you're sick with something contagious in a shared enclosed space like a liveaboard's salon, please stay away from others. A mask can help contain your germs.
However, based on your comments, I guess you have always worn a mask when you had ANY symptom of a respiratory illness regardless how slight???
For me, If I was sick I would stay in my room and away from others when on a LOB and always would have done that. I've cancelled trips and dive days due to cold/flu in the past and would do so in the future.
With respect to LOB's, it sounds like they are not for you as you want zero risk. I'll take my chances, and get good trip insurance to cover the $ loss if there is an issue.
BTW - drop the lecturing/accusatory attitude when you know nothing about the folks you are responding to...