I guess I can understand the point of that, where after someone has offended you, you really don't want to have to sit there and hold their hand and drag it out; but sometimes people really don't know why what they said is offensive.
There are some things everyone should already know not to do or say, but there are a lot of things you wouldn't know if you were sheltered or didn't grow up in a very racially diverse neighborhood-- or at least not a neighborhood with the particular race you're offending.
I think it shows strength in someone if they can, after having been offended, if they find the person truly did not understand what was wrong with that statement, turned around and had the patience to explain it to them. I know on more than one occasion I've pulled the "if you don't know what you did wrong, then I'm not telling you", but I've realized over the past few years that this method doesn't help anyone. It just makes both parties angry and sometimes the person really doesn't know.
I think to be mature adults we have to be able to have an open dialogue about what particular things offend us (but also, to do it without just calling everyone vulgar names and insulting their intelligence, like you said in the original post).