I'd say that the reason why games involving murder seem "more ok" than those involving rape is because everyone already agrees murder is bad in all (real) circumstances, and there's no ambiguity or equivocation about it.
Sadly, that's not the case with forced or coerced sex. Many people will still just consider it "boys being boys," or look the other way if the rapist is a star football player for their local team with a promising future. There are hundreds of stories out there about women and girls who were silenced, ostracized, or worse to protect their rapist - sometimes by entire towns or communities.
The truth is, while some might argue that murder is worse than rape, it is undeniable that rape is a much more sensitive subject than murder.
Sort of like how it's not as bad as murder to, say, mock the mentally challenged or disabled. It's not as bad as murder to be loudly, vocally racist.
But you will hear a whole lot more outcry if and when games are made that involve doing those things.