What to do about dangerous or malicious advice in an answer?

Question

I recently flagged an answer because I (erroneously, as it turned out) believed it to cause harm. The flag was declined on the ground that the purpose of a flag is not to judge technical content. Agreed. However, what if the advice really causes harm (say, it bricks a device)? What about malicious advice as in the following scenario:

Q: I am a newbie and I need help on xyz.

A: yada yada yada ... and rm -Rf / will do what you need.

Answer 1

The site has only a few moderators who handle all the flags, and while they're all fairly knowledgeable folks, they're not expected to be (nor are they) competent technical reviewers for any arbitrary question on the site.¹ It's pretty reasonable to ask them to handle obviously bad advice (like your rm -Rf / example²), but that's obvious trolling. Moderators should delete trolling and ban trolls.

But there are plenty of harmful answers that are given in good faith, and may require specific expertise to spot. If we asked our moderators to deal with those, they'd probably wind up trying to find some experts to ask. But if you can find a few experts to ask, you don't actually need the moderators—the experts can just downvote it, leave comments, etc. And just as importantly, they can write and/or upvote good answers as well. So, generally, we don't expect our moderators to deal with that.

Here's what you can do when you spot an answer you think is harmful, but not trolling:

1. Downvote it.
2. Leave a comment explaining why it's harmful.
3. If you feel strongly about it and/or its very harmful, and you have sufficient rep (2k+), edit the answer to warn the reader to first review the comments. Just a note to make sure the reader is aware of the comments—don't try to start an edit war with the author. With <2k you could try to put that through the edit review queue, but I'm not sure how it'd fare.
4. Ask about the question on #/dev/chat to get more people to review (and vote on) the answer.
5. Ask about the question here on meta, again to get more people to review and vote on the answer.
6. At this point, if it's agreed to be harmful and somehow hasn't already been voted into oblivion, I suppose a moderator would probably be willing to delete it.³

Of course, most of the time you see an incorrect answer (even that is harmful in that it wastes everyone's time), you don't get past steps 1 or 2. You should only very rarely get to step 5.

There are some special cases that a moderator might be willing to delete earlier—e.g., if we got a highly-voted, wrong answer migrated from a larger site. It could take forever for us to outvote the migrated votes from Stack Overflow or Super User, for example.

^{1If they actually are, I have a few unanswered questions I'd like to flag for moderator attention.
2Actually not harmful with a semi-recent coreutils.
3I'm not a moderator, so I can't say for sure.}

Answer 2

OK, if it is something truly dangerous like deleting the EFI firmware or something, that should probably be flagged. For other things, just downvote and/or leave a comment explaining why the command is dangerous.