Tasting notes are rarely rude. At least, in the pejorative sense, they're not. Tragically, they are still sometimes rude in the suggestive sense, employing furtive, salacious phraseology that objectifies the female body with desperate schoolboy lechery. The authors of such notes merit the same treatment as slack-tongued, boggle-eyed, leg-humping dogs: castration.
I'd hope that needs no further explanation. The reasons why tasting notes should not be derogatory about wine are less justifiable, however.
The main excuse given - and I use this myself - is that there is no need to be cruel or disparaging about a wine, even one you strongly dislike. Unlike for music or film, wine reviewers routinely find themselves face to face with the producer, usually in a socially amenable setting, and usually at the producer's expense. Being unnecessarily unkind to a wine in a review releases a stinking, unacknowledged fart of unpleasantness in such situations.
Furthermore, cruelty for its own sake is decidedly unconstructive. Firstly, wine is entirely a matter of subjective taste anyway, so something I might call dilute, sulphurous and volatile might be light, flinty and lifted to you. That means that criticism is better off being tempered, and delivered in a diplomatic mode.
However, there are strong arguments against such submissive politeness. Critics should be free to express themselves howsoever they choose, without fear of rebuke from their targets. This is a founding principle of trustworthy criticism. The first duty of a reviewer is to their audience, not the producer. If somebody thinks a wine is unbalanced, rancid and overpriced, it should be their duty to say so. As a matter of opinion, it is up to the reader whether to believe it or ignore it.
It's also important to show some kind of critical faculty. If wine writers only ever publish positive reviews, their credibility is in question. Knowing what someone doesn't like is equally useful as knowing what they do like. Besides, isn't it somewhat cowardly to rein in your true reaction to a wine in order to not cause upset? If a wine offends your tastebuds, why not offend its creator? After all, they started it.
There are persuasive arguments on either side. My default position remains polite to wines, generally speaking. This is certainly the easier option, not least because being rude about wine risks ostracisation from the industry - or at least, that's the perception. I certainly wouldn't be favourably inclined towards any winemakers who slated my writing. Still, there's only one way to find out ...