Why downvote? I honestly do not get it. 
onoj: I sort of agree with you, but I would only up vote to show that the topic / comment was interesting, even if I did not agree with it . Up/down voting because i agree or disagree is arrogant. If it makes people feel better, bully for them.
The danger is that a group of people will upvote a perspective and alienate alternative points of view from a thread. This creates a narrow minded culture and prevents interesting discussions. Ideally there is no point posing to a thread you agree with if you have no content to add.