What's the reason why a deleted answer, unlike a deleted question, remains visible on the site? Wouldn't it be more appropriate to have it removed once the OP decides, for whatever reason, to delete it?
The main practical reason for preserving (in hidden form) answers that a poster has deleted is, as Rathony points out in a comment above, to enable the poster to reopen the post later. I have occasionally done this when I've posted an answer that a commenter has pointed out has a glaring but correctable fault that requires further research to amend; while I'm doing the additional research, I don't want my flawed answer to draw downvotes from voters who recognize the validity of the commenter's point and wonder why I'm leaving up a bad answer.
As for truly obliterating an answer that seems unfixable and may even be embarrassing, I gather that doing so isn't possible on Stack Exchange sites—certainly not in the straightforward way that obliterating one's own comments is. But you can remove a deleted post from the immediate view of 10,000-rep site participants by following a simple process: Reopen the deleted post, click the edit button, delete the content of the post (or replace it with a message such as "Original content removed."), save, and redelete. At this point, your pinked-out deleted post should show none of the original content of the post you deleted. I can't recall ever having done this myself, but I've seen posts from other users who seem to have adopted this method.
The reason you think deleted answers remain visible but deleted questions do not is because deleted question are more difficult to find. You can still read deleted questions because you have over 10K reps. People with less than 10K reps cannot see deleted posts at all.
It's just that because deleted answers appear in not-deleted questions, you see them more frequently.
All questions and answers were taken from Stack Exchange Meta
Why are answers visible to 10K users?
- How does deleting work? What can cause a post to be deleted, and what does that actually mean? What are the criteria for deletion? [edited May 8 2016]
- What does deletion mean for a post?
Deleted posts are usually not physically deleted (that is, removed from the system); they're just hidden (AKA soft-deleted). This means they won't appear in search results or data dumps, and normal users following links to them will see a 404 (not found) page explaining the cause of deletion.
Moderators, and normal users with >=10k reputation, see all deleted posts that they have links to. Moderators are able to undelete any deleted post.
"10k users" may vote to undelete deleted questions: it usually takes three votes to undelete a question, but sometimes more.
"20k users" may also vote to undelete deleted answers: it takes three votes to undelete an answer.
- Why should 10k rep users view self-deleted answers? [last edited 2009]
In the comment section:
the deletion is to remove clutter, in many cases the action is in good faith and is sensible. Admins (and 10K plus users are effectively a sort of admin by design) can see everything that happens so that, if bad faith, poorly done deletions occur they can be dealt with. What if someone writes abusive stuff then deletes it? how about threats then deletes it. The people doing the checks on this need to be able to see this. –
@ShuggyCoUk Jun 29 '09 at 10:44
- What checks are in place to prevent high rep users and mods from abusing their privileges? [last edited 2014]
The biggest obstacle to abuse is... Everyone. Yourself included. As Tim notes, there's a papertrail for everything - and most of that record is public. Posts, edits, close/reopen, review actions... Even deletion is visible once you have 10K+ on the site. Don't trust a high rep user? Open up his activity feed and keep an eye on him. We can't make everything public, but the more information that's available the better chance there is that someone will catch it. […]
- Deleted questions are sometimes undeleted. Not possible if deletion was permanent.
- Sometimes moderators needs to make a judgement call about a user. The more information they have, the better. Having access to the user's deleted questions and answers can help the moderators make an informed decision.
- Since deleted posts rarely get viewed, they have little-to-no effect on the performance of the site. […]
What to do if you need to "hard delete" an answer or a question
Email firstname.lastname@example.org; they (the devs) are the only people who can truly erase information from all users.
- First, edit out the sensitive information. […]
- Second, flag for moderator attention with "other" flag, explaining why the sensitive information should be removed
[…] Moderators can redact individual revisions to remove all traces of such information from both the post and its history; flagging will alert them to the nature of the problem.