I admit, I'm a bit let down by the consensus in this thread.
Regarding her not answering the asked question, that's pretty accepted as a response on this board. Often a poster will ask how to politely say something, and we advise that the better solution is something else entirely (ask the roommate to move out, not go to the party, etc.)
Regarding the advice to reconsider the tattoo itself, I believe the opinion that tattoos aren't a good idea is just as valid as the opinion that tattoos are a good idea. Neither opinion has to be right or wrong, and it's OK to have either one. (What one does with one's opinion is an entirely different matter, of course).
I think a discussion board and an advice columnist are fairly different things.
First, if one person on a discussion board offers an alternative suggestion Y without addressing the initial question X, then there are plenty more people who may address the original question. Second, on a discussion board, the original poster can easily jump back in and say "I've already decided that I'm not going to do Y [optionally giving reasons]. In light of that fact, how would you handle X?" If no one responds to the question X because they can't imagine not doing Y instead...well, that's a risk you take with a board of regular people having discussions, rather than professional advice columnists. And frankly, if someone here replied to a post about tattoos as Prudie did, loftily lecturing the OP about how tattoos are permanent as if it was impossible that this younger person had thought their decision through, then I'd think that poster was appallingly rude.
Prudence is a professional advice columnist. The typical format for the "discussion" is one letter and one answer--hers. Plus, I'm sure she gets many more letters than she prints in her column, so her choosing to publish someones letter IMO implies a contract to actually give advice on their issue. They are providing her with material to make her living (no letters coming in=no more Dear Prudence), and in return she is supposed to give them useful advice. I don't see a problem with her politely offering additional
advice beyond what the writer asked for (e.g., make sure you've thought this through before you make permanent body modifications, especially if you're worried about the reactions of people close to you). But what she did here was use her soapbox to give a condescending lecture from on high about the evils of tattoos, while offering not one smidgen of advice on how to address the tattoo with the parents.