When I post a question I always try to phrase it in such a way that there are no assumptions implied about the subject I'm asking about. for instance I'd prefer to ask something like "how did the people of Civilisation A view gender" rather than something like "how misogynist were men from Civilisation A?", the latter implies that the people I'm asking about were definitely patriarchal and definitely oppressive towards women. If I can't source an assumption like that I consider it irresponsible of me to include it as it may be incorrect a thus mislead someone reading the OP. if I do have to provide more information to make the question more clear, I'll try to lead into it with something like "as far as I'm aware", IE "as far as I'm aware Civilization A was a very patriarchal society..." , to try and make it as clear as possible that I’m not trying to make a definitive statement of fact.
is it right that I (or anyone else who posts questions here) feel obliged in this way?
phrase it in such a way that there are no assumptions implied about the subject I'm asking about
This is very good practice!
If I can't source an assumption like that I consider it irresponsible of me to include it as it may be incorrect a thus mislead someone reading the OP
I feel the same way!
My opinion is that it doesn't matter too much. What it comes down to is what you, as the one asking the question, want to read in the answer. That you have pre-formed opinions about a subject, likely also means that other people have the same notions - that's how the world works. If you then start off a post with that assumption, it gives the potential replier a hint of where you're coming from, and might also create an interest in the answer from people who shares your own knowledge, but havn't thought about it themselves.
Personally I don't mind reading the replies that start with: "That's a common assumption, but...", or "It/they didn't, however...", and such. I think that, as long as the post is informative, those posts generally turn out to be pretty good, even if it, as you imply, could spread misinformation. Controversely, I really dislike giving those answers myself because it's so difficult to write an answer that at the same time dismisses the thought, but also encourages learning what's right and on top of that is an informative answer in line with what AskHistorians want to provide
In addition to questions, I see comments here pretty regularly that look like someone took an unsourced, anecdotal, or speculative claim and phrased it as a question (e.g. "I've read X" becomes "to what extent is X true"). Obviously there are problems with loaded questions, but I'm not sure if it really degrades the quality of the subreddit: it's easy to identify as non-authoritative information and it solicits further information from an expert.
To what extent are replies like this frowned upon here? Should a distinction be made between first-level and second-level replies?
I don't think you need to feel that way - this sub is all about learning! It's good of you to make the effort, though. I don't mind having to start off an answer by explaining that the underlying assumption is misguided, although I agree with /u/WARitter that it's awkward to say, "... and because your question rests entirely on misconceptions, it's unanswerable."
Hopefully most people are getting their information from the answers, rather than the question, in general.
You could probably have messaged the moderators about this, instead of making a whole new post but in any case, I think your doing it right.