Should Not, Cannot, Do Not Want

I guess things you should not photograph all boils down to your morals.  There's not much of anything that I would feel just should not be photographed, unless the subject is adamantly opposed to the photograph and it's uses.  As for cannot be photographed, I assume the only things that fall into that category is ideas vs. solid objects, though that's where the "concept" part of conceptual art falls.  Every day artists are finding ways to visually represent something that is not visual in nature.  And if we're speaking about physical things that are unable to be photographed because of their nature, I'm sure someone will come along with some technology that will make it possible.  And as for not wanting to photograph, there are many subjects I'd just prefer to avoid.  I tend to enjoy shooting more natural things, as they are, though I never feel the need to go to the lengths of shock art.