Yes this down-vote mania has become more of a problem lately, I agree. As far my opinion is asked I would like to list a few things which will make me down-vote a post or what actions I would take with the powers I have right now.

If a post is duplicate but a well clear formulated question which shows some research effort:

- Flag/Close vote it as duplicate
 - If someone already pointed out it is a duplicate don't comment (one of those is enough, except you think its a duplicate of an other topic)

If a post is duplicate but shows blatantly ignorance to the search abilities provided by the page and Internet:

- Flag/Close vote it as duplicate
 - If someone already pointed out it is a duplicate don't comment (one of those is enough, except you think its a duplicate of an other topic)
 - Leave a comment about the research facilities everyone has at their hands

If a post is duplicate, shows blatantly ignorance and is poorly formulated or even unclear up to it:

- Flag/Close vote it as duplicate or unclear
 - If someone already pointed out it is a duplicate don't comment (one of those is enough, except you think its a duplicate of an other topic)
 - Leave a comment about the research facilities everyone has at their hands
 - Down-vote

I think that should be the proper way to act on such questions, just down-voting because it is a duplicate hurts the sites and Ubuntu's credo.