It is not off-topic --- it should be left alone
I am the author of the answer, so I will explain why the material is not off-topic. The original question refers to COVID vaccine sceptics as "anti-vaxxers" and so my answer spends its first paragraph putting forward an argument for why the OP should avoid using that term in the context of misgivings about the COVID vaccines. That is a legitimate "frame challenge" to an aspect of the original question. It is also an important (and on-topic) aspect of “how to respond” because it advises the OP that he is wrong to use a particular term to refer to his opponents in this matter. It is long-standing policy on Academia.SE that answers may challenge and critique premises of a question, and this is on-topic.
My argument for why the "anti-vaxxer" term should not apply necessarily delves into the differences between the process for the COVID vaccines, relative to the standard approval process for long-standing vaccines. The thrust of the argument is that there are substantial differences between the regulatory process and evidence level for the COVID vaccines compared to long-standing vaccines that have been the targets of people who could reasonably be called "anti-vaxxers", and so the term ought not be applied to people who show misgivings about the COVID vaccines but no broader misgivings about vaccination per se. The reasoning for this argument cannot be made clearly without referring to the differences between the two cases, and this necessarily entails giving at least some broad exposition on evidentiary/regulatory differences.
Now, the “controversy” of this answer is clearly rooted in substantive disagreements about the evidence and regulatory process pertaining to effectiveness/safety of the COVID vaccines, and not in any issue relating to SE site rules. The present complaint is a post hoc complaint that does not accord with the real reason for the controversy in the answer (and is flawed in any case). Indeed, one of the main reasons this answer generated “controversy” is that another user came on to the comment thread and asserted (in big bold lettering) that the relevant paragraph of the answer was "categorically false" and was "misinformation". I then patiently engaged with this user showing evidence of the fact that COVID vaccines have been distributed under "emergency use authorisation" (EUA) instead of the normal FDA vaccine approval process, and expert peer-reviewed medical literature saying that the EUA process is less stringent than the regular vaccine approval process. Readers can review the comment thread for the post and see the argument on this matter if they wish; it confirms that the assertions made in my original post are factually correct and backed by expert evidence, including FDA guidelines and releases, medical literature, and regulatory commentary.
Whilst vote tallies of the answer are not a valid basis for assessment of whether an answer complies with site rules (e.g., whether it is on-topic), at the time of this answer the vote tally is at +20 - 28 = -8 --- i.e., about 42% of voters on the answer have upvoted and about 58% have downvoted; hardly a sign of an inherently low-quality answer. The heavy downvoting is clearly motivated by substantive disagreement with the position (or in my view, with the “feel” of the position) rather than an assessment that the opinion is off-topic or breaches site rules.
Mere controversy of the answer is not grounds for removal, and I believe that I have shown that the answer is on-topic (responding specifically to an aspect of the framing of the original question) and is a legitimate "frame challenge". The alleged precedent for altering or deleting the answer here is not a precedent at all, since it involved assent by the author, which is lacking here. Removal would effectively establish the precedent that an on-topic answer (with +20 upvotes) can be deleted by moderators merely due to substantive disagreement by noisy users. The answer should not be removed.
Re the attempted edit (and any other suggested edits): As I noted when I reverted the edit by @cag51, I think he had good intent in that edit, and his substitute paragraph did not misrepresent my views, but it did strip out the reasoning for why I oppose the use of the term "anti-vaxxers" in this case. I sincerely appreciate his genuine attempt to deal with the matter without misrepresenting my views, and I have nothing but positive things to say about his actions here. While I am open to looking at other proposed edits, the "ship has sailed" on the downvotes/controversy, so I would not be inclined to support edits that remove the reasoning for the position against use of the term "anti-vaxxers". Obviously my position here is likely to lead to a stalemate, since any proposed edit is probably going to want to get rid of this part, and I think it is important that it stay, to show the reasoning for my critique of the premise of the OP. As I have noted above, the reasoning here is directly relevant to a premise challenge to the question that forms part of the advice of “how to respond”.