Claims that certain usages are "bad" because they supposedly create ambiguity are sometimes overstated. But sometimes they're not overstated -- sometimes a term seems to be used in a certain way that's both wrong according to the dictionary, and likely to confuse. Consider this paragraph, from the New York Times "A Call for Manners in the World of Nasty Blogs" article:
Mr. Wales and Mr. O’Reilly were inspired to act after a firestorm erupted late last month in the insular community of dedicated technology bloggers. In an online shouting match that was widely reported, Kathy Sierra, a high-tech book author from Boulder County, Colo., and a friend of Mr. O’Reilly, reported getting death threats that stemmed in part from a dispute over whether it was acceptable to delete the impolitic comments left by visitors to someone’s personal Web site.
Now "impolitic" is defined by the Oxford English Dictionary as "Not politic; not according to good policy; unsuitable for the end proposed or desired; inexpedient." The relevant definition of "politic" is "judicious, expedient, sensible; skilfully contrived. Note that this means something quite different from "impolite."
Yet in context, it seems unlikely that Sierra would have deleted comments because they were injudicious, inexpedient, not according to good policy, or unsuitable for the end proposed or desired. It's possible she might have deleted them because they were senseless, but probably not because they just weren't sensible. It's also possible she might have deleted them because they were so unskilfully contrived as to seem incomprehensible or cranky, but again probably not because they just weren't thought through very well. Given that the debate is about politeness online, that comments are deleted fairly often because they're rude, and that comments are (to my knowledge) rarely deleted because they're injudicious or inexpedient, it sounds like the article author (or an editor) meant to say "impolite" and instead said "impolitic."
Yet what if Sierra did delete comments because they were impolitic, not impolite? My sense is that even then the term "impolitic" would be suboptimal, precisely because it might lead some readers to wonder whether there was an error (and lead other readers to fall prey to the error themselves, and read "impolitic" and "impolite").
Perhaps writers shouldn't have to worry about reader error or about reader misperception of possible writer error. Maybe if "impolitic" is right, the writer should be free to use it regardless of the possibility of confusion. But I doubt it: It seems to me the job of a writer, and especially a journalist, to try to avoid misunderstandings, even misunderstandings that stem from a misunderstanding of a statement that's literally correct (or erroneous suspicion that the statement is incorrect). There may be some exceptions, for instance if you're deliberately playing on the similarity of the words in a way that's amusing, insightful, or memorable; but I see no such justification here.
So if context makes the reader expect a reference to "impolite," but you're really trying to say "impolitic," better to use some suitable synonym for "impolitic" (injudicious, inexpedient, or what have you) and avoid the possible confusion, including confusion about whether you are confused. Better still would be to be more concrete and precise, and explain (briefly, of course) exactly what the impoliteness or impoliticness consisted of, thus avoiding confusion and at the same time avoiding vagueness.