As Ravexina says, I think this is about that answer, which appears intended to work on Ubuntu, but which discloses that it was tested on Fedora. Considering that it would not be considered a moderation issue if the answer had merely not mentioned it was tested at all, I don't support deleting that. What this comes down to is an issue of correctness, and as Kulfy says, that's what votes are for.
But I admit there is some support for your position (though not from the help page on what questions people can ask). It is good you've posted about this. I've been somewhat aware of this issue for a while, and I should've posted myself. I think deleting answers for mentioning they were tested on another distro is a very, very bad idea, and that a policy that all answer authors must test their answers on Ubuntu would support deleting an enormous amount of valuable, highly upvoted content on the site. But I also acknowledge that my view may be in the minority, and that this is not my call to make.
When answers are wrong
It is frustrating when an answer is invalid for Ubuntu.
Of course, most answers that are invalid for Ubuntu don't have anything to do with other operating systems, and don't mention any other operating systems. They're simply wrong answers. We get a lot of wrong answers. We get a lot of answers that are not tested, or not fully tested, or not tested under the specific conditions the OP had. Many of these are wrong answers. Many others are not wrong, and it is often not feasible to reproduce every aspect of a problem the OP had.
Ask Ubuntu, being a Stack Exchange site, is built from the ground up with a mechanism to address answers that are wrong, misleading, or otherwise low quality: downvotes. (It is also useful to comment and, when an answer can be improved without radically changing its meaning, to edit.) Upvotes are the main way to indicate that an answer is correct and useful, and downvotes are the main way to indicate that an answer is wrong or not useful.
Of course, you might consider it harmful or unfair to downvote an answer that could well be right and that you have no strong reason to think is wrong. But if that is the case, outright deleting the answer is far worse!
When answers don't even try to answer the question
We should interpret questions as being about Ubuntu when it is reasonable to do so, and we should close them when it is not. We should judge answers based, first, on whether they're even attempting to answer the question they're posted on, and second, whether they succeed in this goal. I think--and this is my opinion, not an established policy--that there is a big difference between:
- an answer that is intended only to work for some operating system other than Ubuntu and is thus not even an attempt to answer the question it was posted on.
- an answer that is intended to work on Ubuntu but discloses information that suggests it might not.
In my opinion, the first is NAA--though occasionally it could be fixed by editing--but the second is just fine. As a matter of moderation, we don't actually require that people test their answers at all. If someone has tested their answer on Ubuntu, that's good, and it speaks to the quality of their answer. If someone has tested it on some other operating system, that's less useful, and sometimes not useful at all, but it doesn't mean their answer is not intended to answer the question that was asked. Furthermore, it's a good thing when answers disclose possible shortcomings.
This site is based on the idea that we, together, are reasonably capable of judging whether answers to questions about Ubuntu are correct. This is something we're in a good position to do, because most of us use Ubuntu and have some knowledge of Ubuntu.
We're not in a good position to judge other operating systems, whether for similarity to Ubuntu or otherwise. For example, you've proposed allowing answers that mention Debian specifically. What about other Debian derivatives? What about unofficial Ubuntu derivatives? Furthermore, how similar or dissimilar Ubuntu is to another OS depends on what topic is being asked about. Fortunately, knowledge of other OSes is not needed to judge whether an answer is correct for Ubuntu.
...but our existing policy may actually support your position.
Considering that I am constantly going on about the importance of community consensus and the value in citing existing policy, it would be bad--like, real, real bad--if I failed to mention that, at least at the time of this writing, the existing community consensus on this issue appears to favor your position and not mine.
On the one hand, I think the answers to the meta question you cited here, Are answers specific to Debian on-topic?, actually support my view. They're about what OS an answer actually applies to, not merely whether or not it has been tested on Ubuntu at the time it was posted.
But on the other hand, as Ravexina pointed out, we have the more general question What should I do with answers about other Linux distros?. One answer (by TheWanderer) has decisively more votes than any others, and it basically supports your position on this. It begins by saying:
I tend to follow the same mentality I use for questions. Questions about Mint, Kali or even macOS could be perfectly applicable to Ubuntu, but I don't know that, and so I flag as OT. There are specific rules about this for questions, but I use this reasoning to explain my decisions if needed.
An answer that's based off of RHEL, Kali, Debian, etc could certainly work perfectly fine on Ubuntu, but there's no way to really know unless you or the OP tests it. For most cases, I'd flag the answer if it said something like "this worked on Fedora..."
Now, I really strongly disagree with this. Answers are not questions--to answer a question, we have to know about the system the OP is using, but to judge an answer, we have to know about Ubuntu. So a question about a non-Ubuntu OS is actually about a non-Ubuntu OS, while an answer tested on a non-Ubuntu OS may still be an attempt to answer a question about Ubuntu. Furthermore, the need to actually check if an answer works is in no way limited to answers that-- Well, it is in no way limited at all.
But perhaps this criticism is too harsh, considering how that answer then goes on to carve out a major exception:
However, there are cases where an answer might be all-round Linux
applicable. If it's something like:
Q: How do I copy a file from a to b in terminal?
A: I use RHEL, and this is what works:
sudo cp /file /dir/
Then the RHEL is pretty much irrelevant. Something that simple, it
doesn't really matter what distro the answerer uses, since it's
definitely applicable to Ubuntu.
Something more complex, like VNC/RDP, should probably only get answers
from Ubuntu users.
It's challenging to apply this recommendation, because the one example it gives of something that's the same on all distros is a textbook case of something that is not the same on all distros. Not all distros ship with, or recommend,
sudo. Furthermore, the example mentions CentOS. I haven't used CentOS in a while, but last time I used it,
sudo quite deliberately did not work out of the box.
Deleting all answers by authors who aren't Ubuntu users is not something anyone seems to support. But deleting many such answers, while trying to protect others that seem obviously okay, appears very popular. In that answer, simplicity was the guideline. In what you've proposed, distro similarity is the guideline. But I think it is precisely that kind of judgements that go into such policymaking that we are ill-equipped to do here, and precisely the kind of judgments that go into commenting and voting on possibly wrong answers that we are well-equipped to do here.
I don't think I'm the only one uncomfortable with this. I believe that policy is rarely applied, and even more rarely cited. But that doesn't make it right for me to simply ignore it.
A disturbing trend
I see efforts to flag and delete answers that mention they were tested on another operating system as part of a larger trend of using flags and delete votes in place of downvotes. I'm not saying this is something you often do, but I am saying it's something that gets done a lot on this site.
It has become common that I see an answer I know to be correct that has been deleted on the grounds that it's clearly wrong. I often edit these answers to clarify them, and vote to undelete them (or flag them if deleted by a moderator, since then the system doesn't let me cast an undelete vote).
But I also just ignore a lot of them. I have to pick my battles. It takes a lot less time and energy to cast a delete vote or raise a flag, than it takes to edit a post and then explain why it should be undeleted. And that's just the ones I happen to know are correct.
I wish, at minimum, that people would stop trying to delete things they aren't even comfortable downvoting.