You make a good point here.
There is no /r/darkjokes, but there is an /r/darkhumor, so I did take a look at that. I actually think the absurdism metric still holds up here.
This post : "Bastards kicked me out of the library! Apparently I can't put the women's rights books in the fiction section."
53% upvoted. It has 1 upvote. I also think you're right; I think people are overly sensitive to jokes with certain subject matter, and I think that does color our perception of jokes like this. This joke isn't inherently demeaning to women, you could interpret it by assuming you're supposed to be laughing at the fictitious person telling it because they hold a view which is laughably false, but I think it's so controversial because it's about an issue which is still present and it's not 100% unambiguous.
This post, however, did considerably better in spite of the fact that it's about murdering hundreds of people, which is arguably worse than putting a book in the wrong section:
http://www.reddit.com/r/DarkHumor/comments/2sceju/yeah_yeah_but_who_won/
And it really is an absurd situation. I mean let's start with the idea of a contest to kill 100 people with a sword; that in itself is absurd enough, then you realize that OP is just worried about who won? Even though it actually happened, The idea of such a contest is just so far outside the realm of what we would consider believable that it is incredibly absurd.
And no, you're really not alone in thinking that, but being in the majority doesn't necessarily mean being correct. I'm not trying to convince you that the joke isn't funny, clearly it is funny to several people. I'm just saying I think it's a bad joke because it makes light of something which is still a serious issue. There's nothing inherently wrong about making a joke about something dark, but the dark thing you're joking about has to be sufficiently absurd in order to be funny.
I think there are a very small number of people who upvoted this because they're entirely in agreement with the doctor, but you're also right that it would be absolutely insane to assume everyone who upvotes this fits into that category. It makes much more sense to assume that people upvote it because they're not aware that domestic violence is still a serious issue, so it does seem absurd to them.
But that's kind of precisely my point: I think this joke is bad because it reinforces the idea that domestic violence isn't worthy of serious thought, and by presenting this joke in this form, OP is showing that he thinks domestic violence is unrealistic enough to be worth making light of in this way.
Following that, in theory there is a way to improve this joke:
The idea we're trying to make fun of is still too close to an actual serious problem; if you want it to be funny, you must make it absurd. Blow it out of proportion. Take what's already a serious problem and make it just insanely unbelievable.
The problem with that: At this point, we can't really get much more unbelievable than reality.
For example, I discussed the whole Ray Rice thing with people I work with, and found that most of them blame his wife because she was "provoking him" by yelling at him. If you want to argue that she hit him first, you can, but what's important in this discussion is nobody at my work knew that, and they still thought she was at fault. I also used to think jokes like this were funny because I thought surely no sane person would ever think that way, but it's not as uncommon as you'd think.
And in other news, women in India are routinely raped, then stoned for having been raped. This isn't a daily reality for most people, especiallyi in the Western world, but it is still a serious issue. In order to be significantly more absurd than reality, at this point I feel like you would have to make a joke about women and men living on different planets, and one of them building a goddamn Death Star and obliterating the other planet.