I think a better approach than doing away with the notion that obviousness is bad (because, to be honest, if something really is obvious to you, getting a detailed explanation of it can be very annoying), might simply be to explain concepts like inferential distances and mind projection to posters who don't seem to understand them. If people understand those problems of communication and others like them implicitly, they can more easily allow themselves to say something that might be obvious. At least it works that way for me. I won't explain seemingly obvious preconditions of a discussion unless called upon to do so, but I do my best not to assume that everything that might be obvious, is. There are usually plenty of clues. Even if it sometimes requires someone eventually saying "Uh, what does that mean?"

Maybe I'm being terribly optimistic. In my example of one, however, knowing that I have knowledge others might not share is usually enough to make me check if they understand me instead of making the supposition that they do.