That said, I can think of some extraordinary methods for making things disappear for good, in increasing order of difficulty: having a moderator merge your question with another question (needs a really good reason), asking the people who run the underlying database to delete the record (needs an even better reason), filing for and obtaining an injunction in a court with jurisdiction, hiring a team of commandos/hackers/terrorists, airstrike, orbital bombardment.
]]>I think the consensus is generally that deleting content in a way that causes others effort to be wasted is inappropriate. (For example, if your answer is wrong and someone comments to this effect, it's probably better to either respond to the comment, or edit the answer to indicate you now think it's wrong.)
The legal situation is, I think, that by posting you agree to license your content under the GFDL, meaning that you couldn't attempt to use copyright law to prevent distribution of your content.
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