If a word can mean it's exact opposite, literally, then that word no longer has any value, literally.
A handy list of examples: http://en.wikipedia.org/wiki/Auto-antonym
That's not the same thing. The fact that "citation" happens to both mean a commendation and a court appearance is not even "opposites". Those are terms that have multiple meanings, some of which are amusingly different. The word "set" has a billion meanings and I'm sure some contradict each other.
Language misuse impairs communication by introducing ambiguity where there was none.
When I say, "you just bought literally the best card in the game", do I mean it, or is it just a really good card?
When people use "chronic" to mean "acute" instead of "long-term", it makes the term "chronic pain" ambiguous. When people call every headache that hurts a little bit more a "migraine", it diminishes the impact of what a real migraine is.
When I use the word "flaunt", are people like Jimmy Carter going to misread it as "flout"?
I can't use "disinterested" with its real meaning any more, because people will think I mean "uninterested". I have to use another term, none of which captures the same meaning as "disinterested". It doesn't really mean neutral, or even-handed. It means "without a fish to fry". What other word works?
I just don't understand why people are so accepting of bad language usage. Over time, trends change, and we can't help that. But that doesn't mean that every particular bastardization of the English language is OK or should be encouraged.