Fair question.

My feeling is that if we have N sections, we will have e^N arguments (or at least considerations) about posts being in the wrong section. Of course, by this logic, we should have only one section.

And indeed, I think we should following Carter's Compass toward having only one section. With posts differentiated by keywords/tags. And, as I've said, the 'title' field serves as our keywords field. Not that this is ideal, but it's fine. And as long as we don't have a true keywords field, with properly controlled vocabularies, we use sections as essentially a controlled vocabulary for one facet of the post.