It causes damage to our ability to communicate our consciousness. For all we know, people with brain damage (and who are sleeping, unconscious, dead etc.) may be conscious, but just unable to communicate it with us (or remember it when they wake up

This isn't really the sort of thing that Shminux is probably talking about. People with many kinds of brain damage fully retain their ability to communicate, while various faculties for thought associated with those brain regions are affected. Or, on the other hand, regions associated with language can be damaged, leaving subjects impaired in their ability to communicate, while other faculties for thought appear to be largely intact. Brain damage does not simply amount to leaving our consciousness "on" or "off."