I'll start by just making sure we are on the same page. The HW&E tag (which I'll just call the homework tag) and the closure using the "homework-like" reason are
- two distinct things, and
- not reserved only for questions that were explicitly assigned as homework.
I point this out mainly for the comment of "I would like to say I don't ask questions that are homework because I don't have any teacher that can give me homework."
Onto addressing this post then.
And if you look at the question itself, nothing about it seems homework-type.
Not necessarily... I have worked out problems similar to this before. I would argue the question isn't asking about understanding a physics concept; rather, it is asking how to prove something about a physics concept. In other words, it looks like the OP wants someone to do the work on this for them rather than understand something like "what is the appropriate conditions for a trajectory that is an orbit to be made?". It's borderline, but I wouldn't go as strong as to say there is nothing homework-like at all.
indeed the OP sets up a hypothetical scenario from which a conceptual question is asked
This is debatable. If someone posted a question that was something like, "Let's hypothetically say we have a box sliding on a table with friction. Would it be possible for the box to stay on the table? I'm not asking for any computation, it is just a theoretical query if something can happen.", then the question would probably be closed as well. This is because in order to answer the question you still have to show the work of whether or not the box can stay on the table. The post in question is more involved than my example, but the idea is the same. It's not an explicit call to work out the problem... but really the question is still, "hey can you work this out for me?"
I will note that just saying "This question doesn't call for any computation, it is just a theoretical query if something can happen." doesn't mean the question is now safe from being closed as a homework-like question. The intent of the question does not (or at least should not) play a role in whether or not it should be open or closed. A post should be judged on its own independent of what the OP says, their background, etc.
is it even considered ethical to edit-tag a question as a HW type question, to then close it as a HW type question - to give others impetus to also close it as a HW type when they see the tag?
Yes, that is ethical. It's how the site works. Users (with enough reputation) can edit questions how they see fit, and they can vote to close questions. While many questions with the homework tag get closed, getting the tag does not mean "close this question". Ideally, if users understood the site better before posting questions that deserve the homework tag, then actually none of them would be closed, since it is possible to post a question with this tag that is also on-topic for this site. The tag isn't the reason for the closure, nor is it an explicit signal to other users saying, "hey, close this question".
I don't think people other than the OP should add HW&E tags, especially in cases where it is not really clear if it is HW&E since it may lead to unfair closing, as happened in the case above (OP is adamant the original question is not HW&E). For obvious HW type questions, OK. But not in such cases. What do you think?
Something that is unclear to one user may be clear to another. I'm not sure how one would implement a system that lets you change tags only when it is "obvious enough". A hard "other users cannot add the homework tag" is a horrible idea, as it prevents the proper classification of questions in the case where the OP has not (or will not) properly classified it.