"Libertarian" doesn't carve out a very precise cluster in people-space any more. Pretty much anyone who's reflexively wary of government intervention in the private market can call herself a libertarian. Some libertarians will support meaningful government intervention in tragedy of commons type problems; some may even go so far as to support some level of government assisted/coerced redistribution of wealth. You can argue 'till you're blue in the face that that's not a "real" libertarian, but usage defines meaning, and I think enough such people self-identify that way that the word has become fairly imprecise.