Let me quote a very good explanation of the rationale for deleting closed questions:
If a question is valuable enough that it should stay on the site, it should be reopened or fixed into a state that permits reopening. Otherwise, excepting duplicates, it should eventually be deleted if no one expects that it'll be reopened.
If you take the "head on a pike" approach of showing "This is what happens to people who ask what we don't want", it looks rather unsightly. If the problem is because the question is incomplete or broad or something else that can be fixed, keeping it around when someone does not fix it just means you keep what is essentially a mockery of the asker. If the problem is because the question falls outside the scope of the site, then keeping it around invites the problem of users discovering the site because they found that subject matter on the site. The majority of traffic to sites come from searches, so keeping things you do not want people to ask out of sight through deletion helps prevent more people from coming and asking the same thing. "Head on a pike" only really serves as a gruesome reactionary measure than a prevention of the incident.
As such, I recommend that if a question can't be fixed or does not wish to be fixed, that it probably serves the community better if it is deleted. You can give equal guidance to those who run afoul of the rules by pointing at established guidelines - things you write out on the above pages as well as in Meta discussions.
There is a general Stack Exchange policy, expressed in two of Jeff Atwood's blog posts:
But a closed question is no longer alive in any meaningful way, and certainly well on its way to the bit-bucket of /dev/null.
Let me be clear: we do not seek out deletion, by any means. But we believe not having the guts to cull some of your worst content is much, much more dangerous to your community than letting it sit around forever in the vague hope that it will magically get better over time.
Why would you delete a question? Isn’t closing it enough?
- If users see a lot of closed questions, they’ll note that we don’t enforce the guidelines, so why should they? Without any final resolution, asking questions that get closed becomes something we are implicitly encouraging — a broken windows problem. If this goes on for long enough, we’re no longer a community of programmers who ask and answer programming questions, we’re a community of random people discussing.. whatever. That’s toxic.
- If enough of these closed questions are allowed to hang around, they become clutter that reduces the overall signal to noise ratio — which further reduces confidence in the system.
The point of deleting questions is in fine to make the Internet a better place. Closed questions (throughout this post, this does not include duplicates) are questions that have been considered unwelcome here. Off-topic questions are questions we do not have the expertise to answer; our answers have not been reviewed by competent people, so their validity is put into question. Non-constructive or “not real” questions are questions that cannot reasonably be answered; answers to such questions are usually partial and often miselading. Too localized questions do not add value due to highly limited interest.
Responding to your arguments:
- Reputation points are not a consideration when taking moderation actions (whether acting as a user with reputation-granted privileges, or as a diamond moderator). The purpose of moderation is to clean up the site.
- Closed questions are still found in searches. They have exactly the same visibility as open questions.
- I have never seen it useful to have a record of rejected questions.
- When a borderline question is asked, it is best if there is no closed, non-deleted similar question already on the site. This lets the new question be evaluated on its own merits, rather than being summarily lumped with the old question and pressured into sharing its fate.
I do not see why Computer Science should have a different policy from other sites.
Closed questions are not deleted while there is still debate as to whether they should be reopened. After two weeks, I did not see any hint of a debate as to whether Why does Knuth persist with MIX/MMIX? might be reopened. If you think this question can be improved and reopened, answer here or flag it and a moderator will undelete it.