I was thinking... what is offensive? I'm not sure it's actually possible to offend me. There may be things people say that make me angry, but that seems to be a different concept from offense. Some people may say things that make me uncomfortable, but that's not really offense either.
Offense simply seems to be a reaction that people have when reality contradicts their deeply held beliefs. Perhaps "militant delusion response" would be more accurate than "offense."
On this basis, why do we seem to believe that people have some sort of right to not be offended?