Yesterday I voted to delete several old questions that were closed as duplicates. The questions (and the same goes for the targets really) were not a good fit for our site (Ask Ubuntu) and, if they were asked today, could easily be closed there as too broad or primarily opinion based.
It turned out that I'd cast the final vote and one user whose answer had been deleted and who'd thus lost 10 rep mentioned it to me in chat. A passing mod, freely admitting that the deleted posts were "all crap" asked me to refrain from delete-voting questions closed as dupes, and a (nice) discussion ensued, in which I was not convinced to change my practice. I think our mods have differing views on this, so here I am.
As far as I know, closed questions with no upvotes and no upvoted answers will be automatically deleted, unless they are closed as duplicates. This reflects the undisputed fact that duplicate questions can be extremely useful as signposts. I think this is right and good, but I also think that since the system does nothing to distinguish good dupes from bad dupes, it must be my responsibility as a user with >10k to try to clean up the mess, by voting to delete really bad dupes along with other stuff that deserves to go.
The person who disagreed with me argued that what makes a good dupe is basically the fact of its being a dupe:
Good is anything a clueless user might type that could land them on the question. It is impossible to predict what that might be.
To me this idea of good is not good enough. Also, in many cases the dupes have almost identical wording to the target or to other dupes. I totally agree that it's good to have differently phrased versions of the same question around, even better if they have different details that help to show how broadly applicable the target is, or good answers that might, for example, be easier to follow than a highly detailed top answer to a canonical post, but, crap is crap and if we have 20 or 50 or 100 posts pointing to the same canonical post, surely some of the really bad ones are superfluous.
My rationale behind deleting stuff is to have less crap stuff, so people get better search results and the whole site looks better
And he replied
I feel that deleting makes it less likely you'll stumble upon what you're looking for, not more.
My answer to this was (and is) that I don't want anyone to land on low quality posts on our site, even on the way to a better question. I want the site to be awesome and free from crap, as far as I can make it so (many things can of course by fixed by editing, but some cannot). If people aren't landing on the dupe that will lead them to an answer, then, let them ask a new question that we can at worst close as a dupe (hopefully a good one, and at least an up-to-date one). That's not a terrible thing to happen at all, I think.
So, should all dupes be preserved, regardless of quality, or should I vote to delete crap regardless of whether or not it is duplicate crap?