Alternative proposal 1 (and background)
I recently had this happen (screenshot from deleted answers):
This user probably thinks we are a bunch of jerks, or at least that I am a jerk instituting arbitrary rules. And I totally understand why - indeed, after this interaction, it would be very surprising if he thought anything else. And you know what? I hated to see him go, and he will probably never return.
He came, and added what, from his point of view, was a valuable contribution. He put some effort into it, writing a well-formulated text, and added a link to a source. He acted like a good member of the community, as he could not know our unusual stance towards nutrition questions. Indeed, if it hadn't been for that rule, I'd say his post was better than 90% of the first posts we get. And besides, it is one of the cases where the post does not seem to have the potential to cause harm by itself; I thought of leaving it there, but from bitter experience, it would only have created a precedent for other users arguing that, if that nutritional post is allowed, we cannot close their own what-is-good-for-you posts just because they are about nutrition. And they'd have a point.
I deleted with a very curt message, because I was at work and had no time to explain more. The user came back, noticed what had happened, and re-posted the answer, this time adding that the presence of the tag nutrition tells him that we do, in fact, deal with nutrition questions. It impressed me that he did enough research to find that tag, and also that he politely reposted the answer together with an argument for it, without showing any aggression. But the main point was: I had to explain to the poor guy that, we do indeed have a tag called "nutrition", but it is not used to label what most people expect under "nutrition". This is quite surreal to first-time visitors, and it is understandable if it leaves them confused and angry, and they decide to never come back to this (from their perspective) strange and hostile site.
Tags are indeed an important part of our site, and having content tagged correctly enhances finding the right information, which is one of the reasons why we are useful to people. So I normally support having a tag for a distinct category of questions. But I feel that this case is a real exception. Because of the unfortunate circumstances of our tag covering only "the part of nutrition which is not forbidden by our rules", and this fact being completely hidden from users who trust the tags, it does more harm than good.
Renaming it would be a good solution, but as Aaronut points out, anything which is close enough to "nutrition" will suffer from the same problem as the current tag. So, maybe we have to admit that completely removing the tag is the least bad solution available.
The downsides of the tag removal would be:
- we couldn't easily find the questions which are related to nutrition. But maybe this also has a silver lining: if people search for "nutrition" first, and don't find good results, they might be more inclined to believe that we don't deal with nutrition.
- we may end up with questions completely without tags. I hope that these will be isolated cases, and could be dealt with by the creation of tags which are not all that related to the main point of the question, for example labelling a "does vitamin C remain in kale after boiling" question with just "kale". It reduces the information richness of our content, but I think in this case, the loss is justifiable.