I've seen a few examples of people asking low quality questions (usually in good faith), and others answering them (usually in good faith) with low quality answers before the question gets closed. For example. Is there any way to delete an accepted low quality answer? Even if it gets many downvotes, it will still appear in Google, and since the question is closed, there will be no other accurate or high quality answers to contrast with.
Any answer can be deleted by any moderator at any time. If an answer has a negative score, then 20k+ users can vote to delete it. It takes 3 20k votes to delete. If it's really bad, then hopefully three 20k users will catch it after it's been sufficiently downvoted.
^ Yes, we do have a system in place for flagging and deal with the heinously wrong answers.