Why did site participants after so long put your question on hold?
The Stack Exchange structure is one-question/one-answer. It was never intended to be a forum discussion. Please be clear about this: this is not a forum for discussion or debate. In an ideal world, a well-structured question can be answered briefly, definitively, and with supporting references.
Old questions are reviewed as the rules of this (and all other Stack Exchange sites) are created or modified to make the site as valuable and highly participatory as possible. To that end, old questions that are no longer on-topic (if they ever were) are closed to keep new participants from using them to justify asking what today is (or always was) a poorly constructed question. This actually happens and due to limited resources and the natural imperfection of humanity, site participants sometimes require time to close/open questions.
Popularity is not an indicator of a good question or answer. It is only an indicator that a question/answer is of high interest. Popularity is not and cannot be taken into account when closing or opening questions because the purpose of closing/opening is to encourage asking high quality questions and providing high quality answers (both in form and in purpose).
Why was this question closed and why is it likely to remain closed?
I cannot answer on behalf of those who voted to close your question. But I can answer on my own behalf, because I would have voted to close it myself.
The question is too broad.
The question is primarily opinion-based.
This question asks for an encyclopedic answer. It's asking for the responses (moral, amoral, and immoral) of every human being, every community, every organization, and every nation on earth. Answers would be (and were) very long, which (as described above) is not the intent of this site.
Long questions with long answers are difficult for many people to digest. Please don't point to your question's popularity and suggest that I'm wrong. Your question could have easily had 100K visits had people not been forced to spend at least 30-60 minutes reading through everything. Avoiding this situation is the reason one of the justifications for closing a question is that it is "too broad."
Remember what I said earlier, a quality question is one that can be answered briefly, definitively, and with supporting references.
There is no historical incident, scientific theory, or sociological analysis anyone can draw from to give your question as-written an authoritative answer.
And that's the difference between a primarily opinion-based question (no supporting basis at all, we're just offering a pull-it-out-of-the-air opinion) and a good question that draws from the authoritative experience of our site participants to provide an answer.
"But wait!" you might say. "Isn't every question about the effects of magic on a society utterly without everything you just mentioned?"
Yes they are! And that's why we expect those questions to explain in detail the world's rules and limitations. When provided, those rules and limitations allow site participants to provide opinions that are based on the logical structure of the world (hence, "worldbuilding"). The question becomes practical.
Your question has fundamentally no limits. In fact, it went out of its way to avoid basically all limits. There is no structure. How would everybody react? Each according to the dictates of their own morality, ethics, and conscience. I might be able to answer your question on my own behalf, but I doubt anyone knows even their neighbor well enough to answer it on their behalf... much less on behalf of nations.
What do I recommend that you do?
Absolutely nothing. If you start changing your question to try and make it reopenable you seriously risk invalidating all those answers, making the situation infinitely worse. Remember, the purpose of closing a question a long time after it was answered is to stop today's OPs from using it to justify their own question. It's a site-usage quality control issue, not a judgement against the topic of or interest in your question.
As I said in my post, the question is fascinating — but it's also well outside the limits deemed necessary by the "powers that be" to be practical for this site. As I also said in my comment, the only definitive answer would be the size of a book — your book, and the purpose of this site is not to write your book for you.
Finally, before you give in to temptation and start arguing with me about this, please note that I have stood in your shoes. I've complained to the "powers that be" that their rules stink and their treatment of me was unfair. But, over time, I've come to appreciate that they've done a great job of trying to use a service to meet the needs of a very imaginative and creative crowd. My hat's off to them for the quality of their effort. If you peek around in Meta, you'll find that I'm still working with the "powers that be" to better understand what they're doing and why, only now I'm not doing it because I think their treatment of me is unfair — I'm doing it because I want to help people make this the most useful site possible.
And I'm not alone in this. This post was recently created to help OPs better understand how to write a high quality question. I'm referring participants to it more and more.
The simple truth is, the site cannot be all things to all people. Regrettably, your question fell outside the coloring book lines, and we don't want future OPs pointing at your question and saying "he was allowed to do it, why can't I?"
My recommendation is that you (like I had to) salve your wounded pride, come to understand why the site acts the way it does, and work to help others meet those expectations.
And don't think for a moment that I'm not looking forward to your next fascinating question.