Generally it seems when you're asking
You really mean
- Is it a bad idea to do X?
We're about practical problems. If the best thing to do in a given situation is interpreted as rude, it's much more helpful to know what you should do vs "will people like me if I do X".
A problem I noted in the Leaving Early question is that the majority of answers seem to agree almost entirely on what you should do (yeah, leave early, with these caveats), and the difference in most answers is just how rude they find the action as it was (presumably) undertaken. The difference is was really just how and how much they chose to berate the person leaving early or the interviewer, which doesn't really help anyone (but unfortunately is the sort of popular bikesheddery people enjoy).
The practical advice in most of the posts is the same, so the differentiating factor in each post is just exactly how rude they find/assume the behavior to be. That's not really helpful, and what's worse it makes a bunch of practically identical answers superficially different, and turns voting away from "This is a helpful answer" to "I agree with your assessment of the rudeness in this situation".
I would generally discourage "Is X rude" in favor of the "Should I do X?" or "Can I go about doing X successfully?" That's your real question, and there's no room for faffing about with what's rude or not. Maybe you shouldn't do it because it's rude; if that's the case the answers will tell you that. But making the post about rudeness turns it into Bad Subjective territory IMO.
Thus I wouldn't really call it "off topic" but rather "not constructive", in need of some editing to take the focus from subjective, squishy rudeness into more practical matters of what you should really do.