In my opinion down votes serve nothing other than to give spiteful and jeaous people the opportunity for mischief. Positive votes are all that are need for an accurate metric of popularity. Down votes corrupt the true picture, particularly when they are malicious.
Yeah, I share your opinion. I feel almost the same.
There used to be the down voting functionality also in our forum. But they changed the settings and hid it from the screen. I believe it was a right choice. The down voting in forum NEVER help us communicate better. It just causes useless flames.
But I think that the wikis and the extensions need another criteria for rating. It should be less personal. Sometimes I DO want to vote down some wiki articles when they are, say, useless. Although I have never done it, down voting for wikis and extensions has some sense.