The Reddit Down Vote: What's Up With That?

This article is for all you redditors, out there.
I've got a question, I'm hoping that you can help me with the answer, and I'll get right to it: What makes a redditor down-mod a submission? I'll tell you right now that I've Google'd many articles on this particular subject and most of them didn't make any sense to me. There is, for instance, the classic high-and-mighty "yeah, right" that says that an article should only be down-modded if it's written poorly. The theory maintains that a well-written article should be left happily alone - even if one disagrees with its content. Yeah, that all sounds grand and noble, but it's so much twaddle as far as I'm concerned. An exquisitely-written article that provides instruction on baby harp seal killing is destined for a date with the down arrow as far as I'm concerned. Let's face it: Sometimes, content trumps style. But what about other articles? What about submissions that are from all appearances interesting, timely, and even helpful? Why do they get voted down? Case in point: A little while ago, I ran across an article discussing a gene therapy that had been used to successfully reverse sickle cell anemia. Sicle cell anemia! That's a serious problem that is probably faced by millions of people, and here a poster had discovered an article that offered a little beacon of hope. Hope that perhaps many people didn't even know existed. The article had a score of 1. Included in that score was a single down vote. Now, not even dealing with the paltry number of up-votes, how could someone vote something like that down? I mean, that's like voting down a post that announces the discovery of a cure for cancer. What's up with that? I felt sorry for the post and modded it up to protest the injustice - at the same time, asking myself: What in the world goes through people's minds? And here's the kicker: Today I ran across an article that asked readers to download an engine that would allow their computer power to aid in cancer research. That article had a more respectable 4 points (still with 2 down votes, though!). So why was this submission more worthy than the other? And for that matter, what was behind those 2 down votes? Is there a disturbance in the force that I am unaware of? Someone give me a clue, here, because I sure can't beg, borrow or steal a decent one for myself. I got nothin' but the few clues that I've run across in my reading, and they are listed below. Do any of these make sense? Are there reasons that I haven't thought of?

Theories:

1. No matter what the content, new articles get voted down because they are competing with someone else's submission. For the post from user "itsallaboutme" to live, the competition must die.
2. The article touches on a personal pet peeve. I've down-modded one or two submissions that committed this sin, myself, but I can't see how the two above examples apply.
3. Users check out another person's karma to help them make a decision about upping or downing an article. Good is up, bad is down. If this is the case, what's the magic karma threshold?
4. The article is a dupe, and so must die no matter how excruciatingly exquisite the content.
   

Hey, that's all I got, folks. What am I missing?