Recently a question was posted on MathOverflow, which received (I think) more than an average number of upvotes. There was an answer to the question, by someone other than the OP. Next day, the question was deleted by the author (without me seeing any reasons for that), and the answer got thereby deleted as well. I then looked at the OP's page, and he seemed to have gotten a "Disciplined" badge for this action!
It does not seem right to me when a person can so easily delete others' work. Moreover, this seems to contain a serious potential for abuse. E.g., it is easy for one to get an email account, open a new MathOverflow account with it, post a question, get an answer, then delete both, and retain and use the undocumented answer.
I am not sure what would be a good way to deal with this problem. I know that, e.g., once a paper appeared on arXiv, it may be withdrawn but never deleted (as I recall, arXiv says it is done in the interests of good scholarship). Of course, SE's goals and operating model are different from arXiv's.
Yet, I think something should be done to prevent the OP from being able to delete others' work, whether in answers or comments.
Perhaps, more radically, deletions may be abandoned altogether (with poor, inappropriate questions to be placed into some special places, such as the bottom of the list, or into specially labeled folders).
Or am I missing something?