So in this answer, I proposed an alternative idea to JDŁugosz's weapon, now it's obviously hated.
Now, why is it such a big deal to propose an alternative idea, outside the question's scope and put it into the answer, along with the answer?
Your answer is not 'obviously hated'. Sentiments such as dislike or hatred should and have nothing to do with an answer being downvoted1.
The issue with your answer is simply that it is a bad answer.
You're starting it off with some prose that seems to contain bits of information that are a pain to pick out of the unnecessary fluff.
You then continue with a bold & unnecessarily big link to a topic that could probably address issues in the question or even provide a solution to the problem described in the question.
But instead of then elaborating on the subject matter you link to, you seem to drop that thought entirely in favour of what reads as another paragraph of fluff spiked with bits of information that again are made hard to interpret and, from my point of view, make it impossible to even try to understand what you might be hinting at2.
This is then followed by a pseudo-disclaimer that makes anyone reading this feel even more... arsed with.
Then, at a later point in time, you seem to have added a half-hearted attempt at actually providing an answer. But the chosen formatting make it feel even more out of place than the rest of the answer's content.
Why put it in a quote? Is it a quote? If yes, from where? Why is there no source or other text describing where it is taken from or what it is addressing?
Summarized: Your answer is a link to some information, surrounded by distracting fluff. This is not a good answer. It can be argued that it is not even a bad answer, because bad answers usually stem from a lack of effort. The effort you obviously put into the answer is actively distracting from any way this answer could be considered useful, which in turn makes it even worse than a bad answer.
P.S.: I wanted to apologize for any harsh wording. I usually try to do my best to refrain from it whenever I am aware of me using it. But I felt it necessary to bring across the point.
1At least in a perfect world. There's always the odd one out,
but normally the community moderation process does a pretty good job in countering such things.
2Again, if you're even hinting at anything at all, thus theoretically making your answer more than an unnecessarily elaborate comment or pun.
I downvoted the answer and this question because they both demonstrate the same patterns of attention seeking behavior that have been explained to you over and over again.
Both votes had nothing at all to do with offering a different approach as an answer. There's really nothing wrong with offering an alternative approach, provided that the answer still answers the question.
My votes had a lot to do with you being repeatedly offered clear, direct comments and advice that you choose to ignore. People have explained their votes to you at great length over and over again. You're making a conscious choice to ignore them and repeat the same mistakes.
People lose sympathy when it amounts to:
"People keep down voting my jokes!"
When the answer to your problem remains:
"Well... Stop posting jokes."
Bypassing the "why was this specific answer downvoted" as the other two answers to this meta question have that covered and diving into the question part of your question, "is it such a big deal to propose an alternative idea, outside the question's scope[...]?"
No, it's not. In fact, approaching a given question from a slightly different angle has been some of my highest received answers across the entire Stack Exchange network. My brain is sometimes really good at taking that step back and seeing a slightly larger picture and coming to a different conclusion (or sometimes the same conclusion, but one built on an entirely different foundation), but it only happens in that more flexible environment that World Building offers.
My favorite answer is still the one about building a bridge to the stars. It didn't directly answer the question--which had asked about raw manterial--but lead me down a rabbit hole of physics I rather enjoyed having discovered. But it still addressed an aspect of what the asker wanted to know: "how feasible is this?" and as such, had a positive reception.
So no, it's not a problem and sometimes such answers are interesting, might shed light on a question that the asker didn't know they should be asking, but they still need to follow the same direction the question was going. If it's not, then you need to say it's not. "No, you can't" is a perfectly valid answer and from there you can suggest an alternative idea that might fill the role the asker's question fills, but you have to be aware that "no, you can't" is not an answer that people are satisfied with (but sometimes it's the only correct one). So if you're going to say no, be aware of--and be prepared for--some negativity.
All that said, if you misread a question and post an answer that isn't an answer, say "me culpa" and delete it. Move on with your life, you made a mistake. I've deleted more than a handful of my own answers over the years and not once have I felt bitter about it: every time I've learned something new. I've got one answer I can think of (off the top of my head1) that has a net-negative score that I won't delete because my answer isn't wrong it just isn't what someone wanted: I suspect it would have cost them too much work refactoring their code and rather than saying so in a comment, they downvoted my answer. They're free to do that, but my answer is still an answer and still correct; don't take it so personally.
1Checking my list of answers I have ten downvoted answers, two of which are even marked as accepted. One of those is a "no, you can't" answer and was downvoted because the answer was no (all the other answers are basically hacks that "might work" but which "aren't supported," so again my answer isn't wrong, just disliked).
I was surprised by how quickly your post, still in its first version, was downvoted. It was also flagged as not an answer. This was after a period of low traffic on tne site.
Why would people spend their own hard-earned rep to downvote if it already shows a −1 and is in the review queue (so a number appears next to the close link)? My guess is because of your earlier trolling.
The post is disliked because of the in-character answer. The linked Totally Fake… in the first sentence? No, thank-you.
Beyond the issue of not matching the somber and literate style of the venue (you came to a 4-star restaurant dressed as a clown when everyone else is in tuxedos), your meta-question reveals a misunderstanding:
propose an alternative idea, outside the question's scope and put it into the answer, along with the answer?
“along with the answer”? What answer?
Generally, “you can’t” is not a good or well-received answer. If there are issues involving (say) the laws of thermodynamics, concervation of momentum, or logical contradictions in the specification, then these should be (and often are) posted as comments to the question.
If you don’t give a proper justification but just state it’s not going to work, then you are simply saying that you are not creative enough. And indeed, other answers generally show up, proving that.
If an explaination is beyond a comment, containing paragraphs, illustrations, and links; is well-researched and informative; it's still hit-or-miss as to whether it will be well-received. That might be useful to the OP and others who would answer, but don’t try that unless you really know what you’re doing.
Here, you said “isomers gave out excess energy in the form of gamma radiation” which would be the case for naturally decaying samples. The question is how to prevent this from happening! So you’re not even saying “you can’t make such a stabilizer”, you are saying that such rounds without a stabilizer are not good, so what does that even have to do with the question? You completely missed the question!
Note that I’m following my own template from the lessons, so the very first sentence is “… prevents excited nuclear isomers from decaying?” So it’s kind of hard to miss, and others did not, and found your proclamation to be a non sequitur rather than an answer of “you can’t”.