The problem with euphemisms is that people are actually aware they euphemisms, including the people who can't handle reality. Ultimately even euphemism become offensive.

What you're describing is called the euphemism treadmill. The fundamental problem is that you can't get rid something's negative connotation by changing the terms used to describe it, so the negative connotation eventually catches up with the new term. In the case of blacks it would be more productive to ask why that negative connotation is there to begin with and do something to fix it instead of trying to outrun reality with word games.