@user I don't think that your suggestion “answer with a hint, invite to search, then close as duplicate later” is the way to go. (Have you tried it? Have you ever closed a question as a duplicate after giving only a hint? Have you experienced that an asker improved their question, or asked better questions after your tutoring? Links to some examples would be appreciated.)

I have tried to explain my reasons as good as I can. A poor question should be closed. (One can always retract the closing vote if the question is improved – but that does not happen often.) A duplicate should be closed as a duplicate for the reasons mentioned above. (I often leave a comment which demonstrates how I found the duplicate via Approach0, that can help the asker to search themselves the next time.)

I doubt that I can say more (and to be honest, I am tired of the discussion). We'll have to agree that we disagree.

@MartinR Thanks for your reply. Here you can find a recent example of question improved by an asker afetr some hint. I've also other some examples. I'm not claiming that it is always the case but it can really works fine in some cases.

@MartinR I'm not against closure for bad or duplicate questions. As I said, what I claim is that if the scope of closing duplicates is to avoid that more duplicates will raised then the strategy is completely wrong and the result is not different from an answer given by comments or in the proper space. But if there are other reasons which I don't know then it can be fine.

@MartinR Yes I think that we have clarified our positions. We of course disagree about many aspects. My aim was primarly make clear why I claimed that also an imediate closure for duplicates can be against the organization for the site.