What to do with blatantly false answers?

Question

Recently, I came across this answer to an old question, which attempts to prove Fermat's Last Theorem (edit: the answer has now been deleted). It takes almost no effort to see why the argument there is wrong, but somehow, the answer has one upvote and no downvotes. The answer states verbatim:

My investigation of FLT in the last year or so would indicate that there is a simple solution, but you'll need to accept the above constraints. I understand that Wiles' et al solved FLT with out taking advantage of those constraints and made the problem much much harder than it actually is (IMHO).

While this meta post serves to draw attention to this answer in particular, I also want to open a discussion about what we should do when seeing such answers. Unlike questions, which have a better chance of being seen by more people and hence taken down as off-topic, answers seem to be able to slip through the cracks sometimes. In case we see something like this, should we flag for moderator intervention, stating that the premise of the answer is blatantly false? Or should we just downvote and hope that enough people see it (and downvote) to invalidate the answer? Or should we do something else?

Answer 1

I am fairly new on stackexchange and I don't have enough reputation to comment. So, I am compelled to write an answer, although my first choice is to put a comment under your question. But now, that I have enough legroom, I will try to answer it in detail according to my understanding.

My Suggestion: If you (we) come across such answer(s) which are blatantly wrong then you should either provide a better explanation to why that answer is utterly invalid and/or set on wrong premise(s). Sometimes, we infer that something is wrong, but can't provide better expression to our thoughts to write a nice counter comment (or answer), at that time we can downvote and bring answer to the attention of the moderator.

You can also bring this answer to the attention of other active members and ask of their view. If they agree then you can request them to downvote and report-to-mod at same time.

Lastly, you can open up a chat with the answerer and debate to why they think it is the right answer. During the process when you elicit more information or explanation then there are chances that they get aware to why their assertion is entirely wrong. Majority of the time they will understand.

After all, no one earns money or benefit otherwise here on stackexchange. Everyone is trying to help a person who comes here with some inquiry/concern/question/query.