I am wondering what users should do if they encounter a question that has already been down-voted for a particular reason. If you agree with the down-vote, should you down-vote the question as well? 

For example, [this question](https://stackoverflow.com/questions/15016643/equals-and-difference-in-java) was recently posted. It was an obvious duplicate, and should not have been asked. So within several minutes, 8 down-votes were cast, and many comments about it being a duplicate were added.

My question is *Why*? 

Don't you agree that after one or two down-votes, the poster would get the point? What purpose does a 8th down-vote serve, other than to embarrass the poster? Is a duplicate question really that offensive? It's not like he kicked a puppy.

I searched the FAQ and could find no guidelines on this. Should there be a guideline for "piling on" like this? Should the site somehow prevent this sort of thing?

One of the strengths of Stack Overflow is that it is self-policing. So many members truly care. 

However, I am disappointed by this type of behavior and feel that it's giving the site a bad reputation.