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?