"There are a number of users who value karma for itself. For them the deleted comment is cutting losses. For users that don't care about karma itself, I think it is mostly a psychological thing. A user may not care about their karma score yet they do care about the feeling of rejection at their words/statement being downvoted into oblivion. Downvotes get interpreted as 'the community doesn't like you' or 'thinks you are an idiot.' Deleting the comment prevents further downvoting/rejection, removes their username, and effectively erases their mistake (outside of screenshots etc.). I personally prefer the edit and admit mistake option that you mention, but people do have their own reasons for deleting." - Kevin Bondelli