Q:

Is this considered bad attitude?

In my post Imagine I'm on a spacecraft that was accelerated to 1.0$c$ could I only move backwards?, I asked something that came into my mind and I wasn't able to find an answer for it here.
After I posted it, the list of related posts (the list under the title before posting didn't!) showed a question what seemed to be the same. I had a look, found there my answer and marked my post as dupe of that one. Now after that was done I'm getting more and more downvotes for it. What might this reason be? Should I have deleted the post instead?

A:

No, you have done the right thing. With some many questions on the site it's very easy to miss the fact that a duplicate exists, and to be fair the site search isn't as great as it could be.
Don't attach too much significance to the downvotes. It's easy to feel that downvotes are a personal criticism, but really they are just a statement that the question isn't appropriate for the site. Personally I don't downvote duplicates just because they are duplicates, though I know some site members feel differently.
Downvoting does remove the question from the site home page, so there is an argument that a question should be downvoted when we don't want it to appear there. Maybe that's why you have the two downvotes.
I believe that it's generally bad form to delete a question. I can't remember the reasons for this, but I'm sure I have seen comments from the moderators that in general questions shouldn't deleted. Just leave the question - there is an automated cleanup process for downvoted questions that springs into life after a couple of weeks.
For what it's worth you should be congratulated for responding to the duplicate link, reviewing the duplicate and deciding that your question is indeed answered by the existing one. Too many people just abandon their duplicate questions and leave it to the moderators to close.
A quick footnote to summarise David's comments below:
I was a bit hasty to suggest you shouldn't delete your question. The Stack Exchange has various checks to detect users who it thinks aren't being serious, and it will eventually block those users from asking any more questions. One of the criteria it uses is the number of times the user asks a question then deletes it - hence my vague memory that deleting your own questions is a bad thing. However deleting one question, or even a few questions, isn't likely to cause a problem. So you should feel free to delete your question if you want to.
A footnote to the footnote:
As it happens the issue of how deleted questions affect your status has just arisen in the question What is the "positive question record"?. This explains why having lots of deleted question is bad.

