Thread:VisualEditor/Feedback/Intention NOT to allow editing of only a single section?!?/reply

This is a very good point. May I add that besides these good reasons, editing section by section can allow to re-think user interface, to bring controls closer to the edited content and in the end to merge the view and edit tabs, providing users with instant read & write experience (see http://ckeditor.com/demo#inline for an example).