I have posted a question which turned out to be a duplicate.
Here is my drab experience:
- I quickly admitted myself its a duplicate within 1 hour of further research.
- I voted to delete the question & flagged the admin requesting immediate delete (I didnt know it was not possible at that time).
- There were 3 users (in the period of 24 hrs) who -1 my question and added a comment saying its a dupe (way after I posted it was a dupe near the heading of the question by editing it).
So, when a question is closed because its' duplicate, why should it have -1 or +1 button?