Emperor Evulz has killed a few innocent civilians, but the time he slept with a woman drunk off her ass, he's considered to have crossed the Moral Event Horizon.
Emperor Evulz has tortured and killed some innocents, but the time he slept with Alice, a sex slave that Evulz believed was a willing prostitute, is considered his Moral Event Horizon.
Downplayed: The punishment for murder is 20 years in prison, and the punishment for raping someone is 21 years in prison.
Justified: Several people consider rape to be a Fate Worse Than Death, so the punishment is greater than the one for murder.
Rape is considered to be heroic.
While fighting Depraved Bisexual Bob, Alice is defeated. She asks Bob: "Are you going to rape me now?" The response Bob gives her is, "You wish", to show that Alice is in deep trouble.
Rape is so common, it's not really considered "special".
Bob raped someone in his backstory, but he feels deeply remorseful over it. He turns himself in, and when he gets out he speeds the rest of his life repenting. In other words, deity being a rapist, Bob didn't cross the Moral Event Horizen.
Just because it happens often, doesn't make it any less evil.
Bob is only good because he repented. Other rapists who never felt any guilt are viewed as scum of the earth.
The Super Hero team is trying to stop Doctor Destructo's Planet Exploder Ray, but stop in order to arrest a rapist instead.
Emperor Evulz does some terrible things on a daily basis, but the moment he sees a mook looking at a woman longingly, he reacts with horror because he thinks his mook will rape her.
The villain committing an act of rape is treated as evil and morally reprehensible, but no more or less so than the numerous acts of murder and torture they had previously engaged in.
Rape is considered to be morally reprehensible, but less so than murder; perhaps a reasonable position given that some rape victims are eventually able to recover and return to normal lives, but a murder victim will never recover from being dead.
The writer feels that this trope is a bit overdone, and seeks to subvert it by having a character commit a rape and then be portrayed as sympathetic later. However, his editor believes that this will cause a backlash from readers and Moral Guardians everywhere, and thus "strongly encourages" the writer to change the story so that the rapist dies a painful death.
The author or a friend/family member of his/hers is a rape victim
Two random mooks are preparing to violently rape a woman in an alley. One looks at the other and says "Isn't it weird how, even though the psychopath we're working for is going to blow up the earth, we're still seen as more monstrous because of stuff like this?" His friend agrees, just in time for the hero to swoop in and violently execute them.
Discussed: "Hmmm... I'm bored with kicking puppies. How about we go the next level and rape?"
Conversed: "Wow... That kind of evil is above and beyond!"
Deconstructed: Because rape is considered worse than anything else, only rape is eventually considered a crime in the setting. Which means that killing people, Cold-Blooded Torture, genocide, killing children, starving people to death etc. is considered perfectly acceptable as long as there's no rape involved.
Reconstructed: People become more reasonable and, even though rape is still a revolting crime, it's not placed higher on the evilness scale than crimes that are just as bad or worse.