
We do know it's one of the most scaring and traumatic events to ever happen to a person. Rape violates a person at such a personal, emotional and physical level whereby in many cases people can't ever come back from. We know this. Why do we keep writing it into gay relationships. The casualness pisses me off. Oh, I raped you, but it's because I liked you. The victim understands. Like what the actual fuck?!

I don't disagree that rape is terrible and it gives fujoshi a bad rep. And I personally really dislike reading it. I didn't enjoy this manga.
But there is a line between reality and fiction and I think (most?) authors understand that line. Most people who enjoy rape fiction do not actually want to be raped. I think there's something about the loss of control or that it's something taboo that some people really get off to. Enjoying those things is fine, and it doesn't mean you don't have a problem with rape culture and it doesn't mean you think it's okay for rape to be normalized or trivialized.
You could argue that mangaka have a responsibility to their audiences to promote healthy relationships, but that's no different than saying horror-genre film makers have a responsibility to portray murder in a less romanticized way. And that's really not the case. Fiction is simply telling a story. The story might be shitty, but it's still just a story.
I just think drawing a hard conclusion about a group of people based on the fictional preferences of a minority is irresponsible. You might as well say that straight men are disgusting because they enjoy murder movies and that means they have no problems with murder culture. Which is obviously dumb.
(Also I'm not just replying to OP but to the general sentiments expressed in all the replies as well.)

There are about a million things wrong with your reasoning. Lets begin with separating fiction from reality. Fiction in a lot of ways projects what the authors ideals, biases, privilege and prejudice are. For example, like how black actors in Hollywood used to be portrayed a thugs and evil villains to the point where a lot of the world started projecting Black Americans as bad people. And that was based on the racism in Hollywood. Google this. Second, women for example being written as weak damsels in distress also paints us a helpless and shows how patriarchal the world is. Movies for the longest time showed pictures of majority men with women in supporting roles painting a picture of the world structure. Asian characters being written as unable to speak just because they can't speak English. They would be on film or books nodding along like some yes man to whatever the white character was saying. It paints a picture of intellectual inferiority. Which is massively wrong and white supremacists. As if learning Chinese, Japanese or/Korean characters among others is a joke. The portrayal paints a massive picture over an entire population that leads to stereotypes.
Fiction can gloss over reality and make it seem normal. You want to know how? Just like how yaoi has used rape so much that you are actually defending it as something okay. Rape has been normalized by yaoi authors. And the worst part of it is that it has not been normalized by gay men themselves. But by straight women who count be further from homosexual males in the spectrum. That means that someone, not from your community, has told your story, but distorted it, adding societal evils and making it seem normal. It shows just how out of touch the authors who use rape are from gay sex and intimacy.
Now lets look at your comparison in terms of horror movies. Horror movies use thrill ad fear to direct a story line. We see people lurking in danger, ignoring warning and getting brutally murdered. We don't see the person hacked to death emerging from all that and hugging the murderer and calling it a misunderstanding coz-I-love-you-so-much-I-couldn't help-but-kill-you.
We are not talking about writing of rape in fiction. We are talking about Romanticism of rape. Rape can and has been written about in ways that illustrate how traumatizing it actually is. In some cases, the yaoi mangaka even use it to have the seme save the hero from a jealous villain. It's only then that it shows how horrible and scary it is. But the authors saying that having feelings for someone makes rape okay or acts a bridge to sex between characters is what's wrong.
My last thoughts, if you say fiction is very different from reality and what is shown here can be okay to enjoy, how about if its something like racism? How about violence? What if those were normalized? Think about a character being beaten to the throes of death by their partner and we proceed to be shown that he just gets violent sometimes, but he loves the partner anyway. How would that feel. Can you still separate those two?
Its so easy to understand why gay men are against straight women writing yaoi. The rape, because somehow, we straight women can not fathom how intimacy among gay people comes about.