Just because the OP thinks an answer is good doesn't mean that it actually is, and this shouldn't deprive the rest of the community from indicating this by voting.
Deleting an accepted answer has been suggested on MSO and declined, although many people seem to disagree with Atwood's explanation. Personally I think that accepted answers should be deletable by the author (I've also answered a question incorrectly, got accepted, and wanted to delete my answer.)
