It is explicitly understood to be doing a favour to the OP: an already-existing answer to a common question is provided instantly.
What would be the harm in pointing out previous answers but leaving the question open to further contributions? If the previous answer really is adequate, it won't attract further responses. If it's not, well, now its shortcomings can be addressed.
Closing duplicates makes as much sense as aggressive deletionism on Wikipedia. It generally means that somebody missed their true calling on an HOA board somewhere.
The purpose of having the answer there is not to solve the OP's problem. It is to have a question answered that contributes to the canon of work. This way, everyone can benefit from it.
> What would be the harm in pointing out previous answers but leaving the question open to further contributions?
Scattering the answers to functionally the same question across the site. This harms everyone else who wants an answer to that question, and is then subject to luck of the draw as to whether they find the actual consensus high-quality answer.
You might as well ask: what would be the harm in putting a comment in your code mentioning the existence of a function that serves your purpose, but then rewriting the code in-line instead of trying to figure out what the parameters should be for the function call?
> Closing duplicates makes as much sense as aggressive deletionism on Wikipedia.
This analogy makes no sense. The Wikipedia analogue is making page synonyms or redirects or merges, and those are generally useful. "Deletionism" is mainly about what meets the standard for notability.
So instead, it's considered preferable that the best possible answer never be allowed to emerge, unless by sheer coincidence the best answer just happened to be the one that was accepted the first time the question was asked, several years ago.
There's really no need for us to rehash SO rules/policy debates that have raged since day one. The verdict seems to have more-or-less delivered itself.
