It's both about the extreme difference in immersiveness, the feedback loop (you're the one that's conditioned to choose to rape for more points for example) and the age of the target group.
Movies and books present a story. I haven't seen any movies or series portraying rape as desirable rape lately, but even if they do, you don't have to identify with the protagonist. In VR, you are the protagonist, always, and actions are presented as if they're actually yours, trying their best to trick your mind into thinking they are.
So yeah, many differences, nothing good about them.
Its funny that people have been actually making these types of arguments since the beginning of recorded history. The argument that entertainment overrides some rational instinct in people and separates them from reality to think entertainment is the same as real life.
It used to be illegal to make movies with a man and a woman in the same bed together because it was thought to create uncontrollable carnal desires in people. Music and television and books used to be heavily censored due to all their corrupting ideas. Dungeons and Dragons was considered satan worship and evil as well. See the Comstock Law. See prohibition of alcohol...
The problem with all of these arguments is that they have ALL BEEN PROVEN WRONG every single time. Porn, beer, cursing in music, violence in movies, playing an immersive tabletop game where you make the decisions... have never once ever throughout all of human history caused your average person to lose their minds. Normal people are capable of receiving new ideas and using them to build a richer world perspective instead of turning into slathering immoral animals at the first chance.
Another infinitely better argument is that this type of entertainment is cathartic and beneficial.
People fulfill desires through a fantasy instead of reality, thereby decreasing the behavior and actually making the world a better place. But that would requiring viewing people as responsible, self-aware, reflective, adults who are capable of thinking for themselves.
Movies and books present a story. I haven't seen any movies or series portraying rape as desirable rape lately, but even if they do, you don't have to identify with the protagonist. In VR, you are the protagonist, always, and actions are presented as if they're actually yours, trying their best to trick your mind into thinking they are.
So yeah, many differences, nothing good about them.