Jejudo, South Korea
Because we can't control the reader. The word itself is already used as a form of profanity (perhaps bad word is more appropriate)-- no one denies this. If we use it in a poem, we have to realize that; we can't say, "But that's not what I meant, I meant it this way," because, essentially, we didn't fully understand the word we are using, right? If we go down that path, we have to stop talking about secondary and tertiary meanings, we have to stop talking about the 'feel' of the poem.
Right or wrong, we have decided not to use these 'bad words' because people are offended by them -- I see no point in telling people that they shouldn't be offended, that we are using the word in the 'correct' way and therefore that's okay.
This means we are necessarily cutting out a certain part of the language, we are censoring ourselves, but that, strangely enough, also creates the opportunity for new ways of expressing ourselves and that's worth the burden, I think.
I like the somewhat ambiguous system we have now, though.