The notion of constructive criticism has great importance here on E2, where the goal is to make the E2 database a high-quality source of information. (No, I'm not looking for an Everything Ideology War with that last statement. Feel free to constructively criticize me though!)
For instance: You see a node and you dissaprove of it for what you feel is a valid reason. You downvote it. You move on. This is terribly unconstructive! This is like getting a paper back from a teacher that you possibly worked very hard on and thought you did very well on only to find that you failed. Not only that, but there is no explanation as to why you failed. How are you supposed to improve? You know you did something wrong, but what?
It's even worse on E2, because there is no way to tell who downvoted you. That means that if you downvote something, it's your responsibilty to notify (/msg works great) it's author and tell him or her what it was that warranted a downvote. If you don't want the person to know who you are, take advantage of the Everyone Project and do it anonymously. Don't fool yourself into thinking that downvoting a bad write-up is improving E2. It's only half of what you can do to truly improve E2.
I have just recently gotten to Level 2 (Novice), which allows me to vote. I have actually tested this theory, and found that people respond very positively to this kind of constructive criticism.