[TRIGGER WARNING: RAPE, RAPE JOKES, RAPE CULTURE]
This isn't new, but in case you were unaware, multiple studies have confirmed that sexist jokes and rape jokes are directly correlated with pro-rape attitudes. Before you jump in with the "correlation does not imply causation" bit, know that either way you look at it, it's bad. Either these jokes cause more pro-rape attitudes, or there are a whole lot of people with pro-rape attitudes already. And since rape apologists like to claim that rapists and pro-rape attitudes are super rare, there's really no winning for them here.
But let's look at how jokes affect the human mind. Many people say they make jokes to help them cope with terrible things. And it's true that making jokes allows you to distance yourself from an issue. For some people, this is an attempt at self-care. But the unintended effects are that you trivialize the issue. And remember that these jokes don't occur on a small scale. Rape jokes have become incredibly common, so even if they did start as an innocent attempt to make something awful seem more distant, the unintended effect is that we have kids on camera laughing about a girl being raped in the next room.
Much more common are various memes using rape as a joke, like the one with the creepy-looking sloth. The fact that this meme often includes an image of half a woman's face, which the sloth is whispering to, shows that these jokes are directed at women in particular, while failing to show the entire face of the woman.
Cutting out the face of a person in an image is a classic dehumanization technique. The language in these jokes is also very dehumanizing. And any basic research on dehumanization will show you how it's been systematically used throughout history to justify horrific treatment of human beings. Jokes have often been used to compare people of color and Jewish individuals to compare them to animals - a direct form of dehumanization. As soon as you can view someone as less than human, it becomes much easier to harm them.
At the same time, trivializing horrific crimes like rape have a clear effect of making rape seem like it's not a big deal. Many teen boys appear to feel that rape is not such a terrible thing. Obviously, if you can joke about it and laugh about it, it must not seem so terrible to you. That's the function of jokes, right? To distance yourself, make something seem not so bad?
And now here we have evidence of correlation between rape jokes and pro-rape attitudes.
So. A lot of rape jokes dehumanize women. They all trivialize the issue of rape. And the only other explanation for the correlation between these jokes and pro-rape attitudes is that people with pro-rape attitudes make the jokes, but there sure are a shit load of men and boys making these jokes.
You have to stretch pretty far to believe that rape jokes don't promote rape. And even if you do, the conclusion you land in is even more horrifying.